Nature Guide_ Rocks and Minerals

ROCKS | METAMORPHIC ROCKS 299 PROFILE Distributed eclogite grains red pyrope Eclogites, such as this one with garnet s Regional red garnet and green pyroxene, t High-pressure are formed under great pressure, and are thought to originate in metamorphism of the mantle. silica-poor igneous rocks 1 High temperatures (1,065°F/575°C or above) 2 High 3 Foliated, crystalline u 1⁄16–3⁄16 in (2–5 mm) v Pyroxene, garnet w Kyanite, quartz, olivine, diopside x Various colors z Silica-poor igneous rocks green omphacite VARIANTS ECLOGITE Mantle rock Eclogite with A rare but important rock, eclogite is formed garnet porphyroblasts only by conditions typically found in the mantle or the lowermost and thickest part of the continental crust. Fine-grained eclogite Its overall chemical composition is similar to that of Garnet- and pyroxene-rich igneous basalt (p.273). It is a beautiful, coarse-grained, specimen of eclogite dense rock of bright red garnet and contrasting bright green omphacite—a pyroxene characteristic of high-temperature metamorphism. Diopside (p.210) and olivine (p.232) are commonly present as well. Eclogite grains may be evenly distributed or banded. Eclogite forms at very high temperatures (1,065°F/575°C or above) and pressures from silica-poor igneous rocks. Many investigators believe that eclogite is characteristic of a considerable portion of the upper mantle. When brought upward into the crust, eclogites are mainly found as xenoliths (foreign inclusions) in igneous rocks and as isolated blocks up to 330 ft (100 m) wide in other metamorphic rocks. Although rare, diamonds (p.47) may occur in eclogites.

300 ROCKS | METAMORPHIC ROCKS PROFILE Soapstone specimen This specimen of soapstone s Regional shows the foliation of the t Metamorphism of original talc. serpentine in presence of water 1 Low temperatures (up to 400°F/200°C) 2 Low 3 Foliated u Less than ⁄1 256 in (0.1 mm) v Talc w Chlorite, magnesite x White, green, brown, black z Serpentine greasy luster massive habit VARIANTS SOAPSTONE Foliated Also known as steatite, soapstone is a fine-grained, soapstone Soapstone massive rock. Talc (p.193), one of the softest minerals, is with visible foliation its principal component. Soapstone specimens are easily Flaky soapstone Soft recognized by their softness: they have a greasy feel and soapstone with a flaky surface can be scratched with a fingernail. Soapstone may also Green contain varying amounts of amphiboles, such as soapstone A specimen anthophyllite (p.216) and tremolite of soapstone consisting (p.219), and chlorites. Specimens primarily of green talc can be green, brown, or black when polished, but they become white when scratched. Soapstone is found associated with other metamorphosed silica- poor igneous rocks, such as serpentinite (p.298). It is used in fireplace surrounds because it Lion dog seal absorbs and distributes heat Soapstone, such as that evenly. It is also carved into molds used in this Chinese seal, for soft-metal casting. has been used to carve ornaments for millennia.

ROCKS | METAMORPHIC ROCKS 301 iron-oxide Marble breccia PROFILE cement This specimen of marble has been cracked and shattered, the veins s Regional or contact infilled, and fragments recemented metamorphic with iron- and calcium-rich cement. t Contact or regional marble fragment metamorphism of limestone or dolomite 1 High temperatures (1,065°F/575°C or above) 2 Low to high 3 Crystalline u Up to 3⁄4 in (2 cm) v Calcite w Diopside, tremolite, actinolite, dolomite x White, pink z Limestone, dolomite hematite vein VARIANTS MARBLE Olivine A granular metamorphic rock, marble is derived marble Marble with from limestone (p.319) or dolomite (p.320). It consists small crystals of olivine of a mass of interlocking grains of calcite (p.114) or the Green marble A specimen mineral dolomite (p.117). of marble colored by green silicate minerals Marbles form when limestone buried deep in the older Gray marble Marble from layers of Earth’s crust is subjected to heat and pressure relatively pure limestone from thick layers of overlying sediments. It may also form as a result of contact metamorphism near igneous intrusions. Impurities in the limestone can recrystallize during metamorphism, resulting in mineral impurities in the marble, most commonly graphite (p.46), pyrite (p.62), quartz (p.168), mica, and iron oxides. Taj Mahal, India In sufficient amounts, these can The Taj Mahal is built of affect the texture and color of Makrana—a white marble the marble. that changes hue with the angle of the light.

302 ROCKS | METAMORPHIC ROCKS PROFILE brown calcite s Contact t Contact metamorphism of limestone 1 High temperatures (1,065°F/575°C or above) 2 Low 3 Crystalline u 1⁄256–3⁄4 in (0.1–20 mm) v Calcite w Garnet, serpentine, forsterite, vesuvianite x Variegated z Limestone, dolomite Skarn specimen diopside and This specimen of skarn with tremolite calcite and dark minerals shows the rock’s typical veined and SKARN banded appearance. This rock is a product of the contact metamorphism VARIANT of limestone (p.319) or dolomite (p.320) by an igneous intrusion, often granite (pp.258–59), with an intermediate Garnet in skarn A uvarovite or high silica content. Hot waters derived from the granitic garnet porphyroblast in a magma are rich in silica, iron, aluminum, sulfur, and skarn matrix magnesium. When limestone or dolomite is invaded by this high-temperature hydrothermal solution, the carbonate minerals calcite (p.114) and dolomite react strongly with the slightly acid solution. The elements carried in the solutions combine with the calcium and magnesium in the parent rock to form silicate minerals, such as diopside (p.210), tremolite (p.219), and andradite. The resulting rock is usually a highly complex combination of calcium-, magnesium-, and carbonate-rich minerals. Skarn minerals can be fine- to medium-grained. They also occur as coarse, radiating crystals or bands. Some skarns are rich in metallic ores and form valuable deposits of metals, including gold (p.42), copper, iron, tin, lead, molybdenum, and zinc.

ROCKS | METAMORPHIC ROCKS 303 PROFILE s Contact metamorphic t Contact metamorphism of fine-grained sediment 1 Moderate to high temperatures (400°F/ 200°C or above) 2 Low to high 3 Crystalline u Less than ⁄1 256 in (0.1 mm) v Hornblende, plagioclase, andalusite, cordierite, and others w Magnetite, apatite, titanite x Dark gray, brown, greenish, reddish z Almost any rock dark, pyroxene crystals Pyroxene hornfels HORNFELS In this specimen of hornfels, dark porphyroblasts of pyroxene Formed by contact metamorphism close to igneous can be seen. intrusions at temperatures as high as 1,300°–1,450°F (700°–800°C), hornfels can form from almost any parent VARIANTS rock and is notoriously difficult to identify. Its composition depends on the parent rock and the exact temperatures Garnet and fluids to which the rock is exposed. Specimens are hornfels usually dense, hard, and hard to break. They are fine- A specimen grained and relatively homogeneous, with a conchoidal, colored red by flintlike fracture. The rock may sometimes appear glassy. garnet crystals The color is usually even throughout, although specimens may also be banded. Cordierite hornfels Hornfels with small grains of cordierite, Hornfels is often categorized by the mix of minerals quartz, and mica present in the specimen. Garnet hornfels, for example, is characterized by large crystals of garnet set into a rock Chiastolite hornfels Hornfels matrix. Cordierite hornfels contains large crystals with elongated porphyroblasts of cordierite (p.223) that can be up to several inches of chiastolite (andalusite) in diameter. An outcrop of hornfels rarely extends more than a few yards from the contact and may pass outward into spotted slate.

304 ROCKS | SEDIMENTARY ROCKS SEDIMENTARY ROCKS Sedimentary rocks are formed at or near Earth’s surface either by accumulation of grains or by precipitation of dissolved material. These rocks make up the majority of the rock exposed at Earth’s surface, but are only about 8 percent of the volume of the entire crust. LITHIFICATION grain settling The transformation of loose grains of grain sediment into clastic sedimentary rock is known as lithification. The grains are water often bound together by a cementing agent, which is generally precipitated from substrate cement Sedimentary solutions that filter through the sediment. aggregations In some cases, the cementing agent is Deposited by wind and created at least in part by the breakdown water, mineral grains form of some rock particles of the sediment loose sediments. Over time, itself. The most common cement is silica these grains are lithified— (usually quartz), but calcite and other compacted or cemented— carbonates as well as iron oxides, barite, until they form solid rock. anhydrite, zeolites, and clay minerals also form cements. The cementing agent been deposited as sediment. In other becomes an integral and important part cases, hundreds or even millions of of the sedimentary rock once it is formed. years may pass by before lithification In some cases, clastic sedimentary rocks occurs. At any given time, there are large (see opposite) can also be formed by simple amounts of rock fragments that have compaction—a process in which the grains been produced by weathering but have bind together under extreme pressure. not been lithified and simply exist as a form of sediment. Lithification can sometimes take place almost immediately after the grains have transported by weathering and erosion water, wind, ice, and evaporite deposits form in gravity basins on land transported by water burial and lithification particles in ocean transport by different kinds of water settle to form ocean currents sediment accumulate seafloor sediments in distinct layers uplift exposes sedimentary rock Sedimentary rock formation The formation of sedimentary rocks begins with weathering and erosion. This creates sediments that are transported to basins on land or to seas and lakes, where deposition, burial, and lithification take place.

ROCKS | SEDIMENTARY ROCKS 305 CLASTIC ROCKS cementing Clasts are rock fragments ranging in size agent from boulders to microscopic particles. Clastic sedimentary rocks are grouped large Conglomerate according to the size of the clasts from pebble Conglomerates are which they form. Larger clasts such as the most coarse-grained pebbles, cobbles, and boulder-sized gravels sedimentary rocks. They consist of form conglomerate and breccia; sand pebble-sized or larger grains, bound becomes sandstone; and finer silt and clay together by a cementing matrix. particles form siltstone, mudstone, and shale. The mineral composition of clastic rocks can be subject to considerable change over time. CHEMICAL ROCKS White Cliffs of Dover Chemical sedimentary rocks are formed Located near the town of Dover in Kent, England, by the precipitation of the transported, the celebrated White Cliffs of Dover are spectacular dissolved products of chemical weathering. deposits of chalk many feet thick. In some cases, the dissolved constituents are directly precipitated as solid rock. Examples include banded iron formations, some limestones, and bedded evaporite deposits—rocks and mineral deposits of soluble salts resulting from the evaporation of water. In other sedimentary rocks, such as limestone and chert, solid material first precipitates into particles or becomes the shells of organisms, which are then deposited and lithified. FOSSILS plants and animals. After an organism A fossil is a remnant, impression, or trace dies, the soft parts decompose, leaving of an organism that lived in a past behind only the hard parts—the shell, geologic age. Fossils are preserved teeth, bones, or wood. Buried in layers almost exclusively in sedimentary rocks. of sediment, the hard parts gradually The most common fossils are of aquatic turn to stone. In a process known as permineralization, water seeps through the chalk surrounding body of clearly visible rock, depositing mineral salts in the pores fossil sea urchin spines of the shell or bone, thereby fossilizing the remains. In some cases, the organic matter is completely replaced by minerals as it decays. In other cases, circulating acid solutions dissolve the original shell or bone, leaving a cavity of identical shape, which is filled in as new material is deposited in the cavity, creating a cast. Fossil in chalk Large sea urchin fossils, such as this well-preserved example, are usually found in chalk, which is itself made up of the fossils of tiny marine organisms.

306 ROCKS | SEDIMENTARY ROCKS PROFILE s Detrital, from pebbles t Marine, freshwater, glacial u 1⁄16 in (2 mm) to several in (cm) in finer matrix v Any hard mineral can be present w Any mineral can be present x Varies y Very rare fine-grained sediment rounded clast Puddingstone conglomerate This conglomerate specimen from VARIANTS Hertfordshire, England, consists of pebbles that were rounded by water Quartz and then cemented together. conglomerate A specimen CONGLOMERATE with large clasts of quartz Rocks formed by the lithification of rounded rock fragments that are over 1⁄16in (2mm) in diameter are known Polygenetic conglomerate as conglomerates. They can be further classified by the A specimen with clasts of average size of their constituent materials—pebble- various rock types conglomerate (fine), cobble-conglomerate (medium), alluvial diamond and boulder-conglomerate (coarse). Conglomerate can Alluvial also be known by the rock or mineral fragments in its diamond composition; for example, a quartz pebble conglomerate. A diamond cemented Depending on the environment in which these into a fragments are deposited, these rocks may be of two conglomerate types. Well-sorted conglomerates result from water flow over a long period. These have well-sorted pebbles (with a small size variation) generally of only one rock or mineral type, and a few small particles between the pebbles. Poorly sorted conglomerates form from rapid water flow and deposition. They have poorly sorted pebbles (of varying sizes) of mixed rock and mineral types with a number of small particles between the pebbles.

PROFILE ROCKS | SEDIMENTARY ROCKS 307 s Detrital, from coarse angular fragment sediment t Marine, freshwater, glacial u 1⁄16 in (2 mm) to 1 in (several cm) in finer matrix v Any hard mineral can be present w Any mineral can be present x Varies y Very rare gray, silica-rich BRECCIA fragment Lithified sediments with rock fragments that are more Poorly sorted breccia This specimen of breccia than 1⁄16 in (2 mm) in diameter but angular or only slightly shows large and small angular fragments with no clear pattern rounded are called breccias. The lack of rounding indicates of orientation. that little or no transportation took place before the VARIANTS fragments became incorporated in the rock. Limestone breccia Breccias can form in several ways. Rocks can shatter— Fragments of limestone for example, due to frost action or earth movement— in breccia and the fragments then become cemented in the new Polygenetic breccia A specimen with clasts of position. Shattered fragments may also move before different types of rock being cemented—for example, they may accumulate at Fault breccia Cemented clasts shattered by faulting the base of a cliff or be carried by a flash flood. Breccias can also form in areas of active faulting. In areas where faulting occurs underwater, newly shattered material can also Breccia vase move in underwater landslides This ancient Egyptian and become cemented to carved vase made of form breccia. breccia or mottle stone was used to store liquids.

308 ROCKS | SEDIMENTARY ROCKS PROFILE Structure in sandstone evidence of This sandstone from Yorkshire, slumping s Detrital, from sand England, is derived from deposits t Terrestrial of wind-blown sand. The bedding u 1⁄256–1⁄16 in (0.1–2 mm) planes, which slumped after v Quartz, feldspar deposition, are well preserved. w Silica, calcium carbonate x Cream to red fine-grained y Vertebrates, invertebrates, texture plants VARIANTS SANDSTONE Micaceous sandstone The second most abundant sedimentary rock after A specimen with flakes of mica and patches of iron oxide shale (p.313), sandstone makes up about 10 to 20 percent Goethite sandstone Sand of the sedimentary rocks in Earth’s crust. Sandstones grains with red goethite are classified according to texture and mineralogical Red sandstone A specimen of properties into micaceous sandstone, orthoquartzite quartz sandstone colored red due (p.310), and graywacke (p.317). They are usually dominated to the presence of iron oxides by quartz (p.168) and have visible sandy grains and other minerals present in varying amounts. Well-rounded grains are typical of desert sandstone, while river sands are usually angular, and beach sands somewhere in between. Bedding is often visible in sandstones as a series of layers representing successive deposits of grains. Bedding surfaces may show either ripples or the cross bedding typical of dunes. Sandstone platform Sandstone is an important This platform in the center indicator of deposition and of the courtyard pool at erosion processes. Fatehpur Sikri, India, is made from red sandstone.

Marine greensand ROCKS | SEDIMENTARY ROCKS 309 This specimen is from the Atlantic coastal plain of North America, well-sorted where greensand is a common sediment type of rock. green coloring from glauconite PROFILE GREENSAND s Detrital, from glauconite- A quartz sandstone with a high percentage of the green rich marine sand mica mineral glauconite (p.196) is known as greensand or glauconitic sandstone. The term glauconite is also loosely t Marine applied to any glauconitic sediment. Glauconite is believed u 1⁄256–1⁄16 in (0.1–2 mm) to form in shallow, oxygen-poor marine environments that v Quartz, glauconite are rich in organic detritus. It forms as a result of a slow w Feldspar, mica accumulation of sediments, by the replacement of calcite x Green (p.114), or by primary deposition. It may contain shell y Vertebrates, invertebrates, fragments and larger fossils. Some glauconite pellets are biogenic, originating as fecal pellets. plants Greensand tends to be weak and friable, although VARIANT relatively hard greensand has been used as building stone. The soil derived from greensand varies, ranging Greensand banding from fertile to sterile. Glauconite is favored in organic A band of greensand within cultivation as a natural source of potassium and a rock outcrop phosphorus. Its potassium content is useful in radiometric age-dating. Due to its chemical-exchange properties, the glauconite in greensand is used as a water softener and in water-treatment systems.

310 ROCKS | SEDIMENTARY ROCKS quartz grains PROFILE Pink orthoquartzite Although this specimen of pink s Detrital orthoquartzite is composed almost t Terrestrial entirely of quartz, it is colored by u 1⁄256–1⁄16 in (0.1–2 mm) small amounts of iron oxide. v Quartz w Heavy minerals, such ORTHOQUARTZITE as zircon and rutile A pure quartz sandstone, orthoquartzite is usually composed of well-rounded quartz (p.168) grains cemented x Light to medium by silica. The high degree of rounding of the grains y Rare, vertebrates indicates that they have traveled some distance, which also accounts for the high degree of sorting. Some VARIANT orthoquartzites are up to 99 percent quartz, with only minor amounts of iron oxide and traces of other erosion- Gray orthoquartzite resistant minerals, such as rutile (p.78), magnetite (p.92), A specimen colored gray and zircon (p.233). Lesser amounts of other minerals can by quartz grains color the generally white or pinkish specimens either gray or red. Orthoquartzites can be differentiated in hand specimens from other sandstones by their lighter color and absence of other minerals. Orthoquartzites rarely preserve fossils, although the sedimentary structures are usually preserved. The presence of silica cement makes orthoquartzites durable. They tend to resist weathering and form prominent outcrops. Orthoquartzite is distinct from metamorphic quartzite, also known as metaquartzite (p.295).

Gray arkose 311 Darker variants of arkose, such as this specimen, tend quartz to be older than pink arkose. grains pinkish feldspar PROFILE ARKOSE s Detrital, from A pink sandstone, arkose is colored by an abundance of feldspar-rich sand feldspars (pp.173–81), especially pink alkali feldspars. Its high feldspar content (more than 25 percent of the sand t Terrestrial, marine, grains) sets it apart from other sandstones. Arkose or freshwater specimens are relatively coarse and consist primarily of quartz (p.168) and feldspar grains, with small amounts u 1⁄256–1⁄16 in (0.1–2 mm) of mica. The grains tend to be moderately well sorted v Quartz, feldspar and angular or slightly rounded. They are usually w Mica cemented with calcite (p.114) or sometimes with iron x Pinkish, pale gray oxides or silica. The flat cleavage faces and angular grain y Rare shape of the feldspars reflect light under a hand lens. Sandstones with a feldspar content of 5–25 percent VARIANT are called subarkoses. Pink arkose A variant of Arkose forms from the quick deposition of sand arkose formed more recently weathered from granites (pp.258–59) and gneisses (p.288). than gray arkose The development of arkoses is thought to indicate either a climatic extreme or a rapid uplift and high relief of the source area. Arkoses are common along the front ranges of the Rocky Mountains.

312 ROCKS | SEDIMENTARY ROCKS PROFILE s Detrital, from grit t Freshwater u 1⁄32–3⁄16 in (1–4 mm) v Quartz, feldspar w Garnet, rutile x White, pink, gray y Invertebrates, vertebrates, plants reddish color from iron oxides Quartz gritstone GRITSTONE Specimens of quartz gritstone, such as this, are composed of Providing material for grindstones and millstones, more than 75 percent quartz. gritstone has, in the past, been a commercially important sedimentary rock. It is a porous rock composed of VARIANT cemented, coarse, often angular sand grains, with occasional small pebbles. Quartz (p.168) is always the Feldspathic gritstone greatest component, but specimens often contain iron A variant containing up to oxides that give them a yellow, brown, or red color. In 25 percent feldspar some, the grains can be easily rubbed out; in others, strong cement makes the rock suitable for use as grinding stones. Gritstones originate in river deposits and frequently show signs of cross-bedding or current bedding. The Millstone Grit, a gritstone deposit in northern England, was mined for millstones used in flour mills and for grindstones, which were used to make paper pulp from wood and sharpen tools. Gritstone is still quarried for use as building material worldwide. Large exposures of gritstone are favored by rock climbers because the rough surface provides outstanding friction, enabling them to grip the smallest features in the rock.

ROCKS | SEDIMENTARY ROCKS 313 Gray shale This specimen of shale from Runswick Bay, Yorkshire, England contains fossils of bivalves and ammonites. fossilized ammonite fissile sheets fossilized bivalve PROFILE s Detrital, from mud, clay, or organic material t Marine, freshwater, glacial u Less than ⁄1 256 in (0.1 mm) v Clays, quartz, calcite w Pyrite, iron oxides, feldspar x Various y Invertebrates, vertebrates, plants VARIANTS SHALE Fossiliferous shale Shale The most abundant sedimentary rock, shale makes with numerous fossils of brachiopods up about 70 percent of all sedimentary rocks in Earth’s alum-rich crust. It consists of a high percentage of clay minerals, mineral substantial amounts of quartz (p.168), and smaller amounts Light-colored shale A specimen with alum-rich, of carbonates (pp.114–25), feldspars (pp.173–81), iron light-colored areas oxides, fossils, and organic matter. Shales are colored reddish and purple by hematite (p.91) and goethite (p.102); blue, green, and black by ferrous iron; and gray or yellowish by calcite (p.114). They split easily into thin layers. Shales consists of silt- and clay- sized particles deposited by gentle currents on deep ocean floors, shallow sea basins, and river floodplains. They occur thinly interbedded with layers of Fossil trilobite sandstone (p.308) or limestone Preserved in gray shale, (p.319) and in sheets up to several this fossil trilobite is yards thick. more than 400 million years old.

314 ROCKS | SEDIMENTARY ROCKS Dark oil shale This specimen of oil shale shows dark, kerogen-rich layers. When heated, the kerogen gives off a vapor that contains oil. kerogen-rich rock PROFILE s Detrital t Inland seas u Less than ⁄1 256 in (0.1 mm) v Quartz, feldspar w Alum x Gray, black y Invertebrates, vertebrates, plants VARIANT OIL SHALE Oily surface A specimen with The name oil shale is a general term for organic-rich condensed droplets of oil sedimentary rocks that contain kerogen—a chemically visible on the surface complex mixture of solid hydrocarbons derived from plant and animal matter. When subjected to intense heat, these shales yield oil. Oil shales range from brown to black in color. They are flammable and burn with a sooty flame. Some oil shales are true shales in which clay minerals are predominant. Others are actually limestones (p.319) and dolomites (p.320). Much of the original organic material in oil shales is unrecognizable, but it is believed to be derived from plankton, algae, and microorganisms that live in fresh sediment. In previous centuries, small amounts of oil have been successfully recovered from oil shales. During the past century, oil shales have been mined with rock types varying from shale (p.313) to marl (p.322) and other carbonate rocks. Various pilot plants have been built to extract oil from shales, but the commercial results have been modest so far.

Gray siltstone ROCKS | SEDIMENTARY ROCKS 315 The tiny grains that make up siltstone are too small to be silt-sized grains seen without a microscope. dark color from carbon PROFILE SILTSTONE s Detrital, from silt Formed from grains whose sizes vary between that of t Marine, freshwater, sandstone (p.308) and mudstone (p.316), siltstone is a sedimentary rock. Like sandstone, it can form in different glacial environments and have different colors and textures. Siltstones are typically red and gray with flat bedding u Up to ⁄1 256 in (0.1 mm) planes. Plant fossils and other carbon-rich matter are v Quartz, feldspar common in darker-colored siltstones. Examples tend w Mica, chlorite, mica-rich to be hard and durable and do not easily split into thin layers. However, the presence of mica may produce a clay minerals siltstone that splits into thicker, flagstonelike sheets. In addition to mica, siltstone may contain abundant chlorite x Gray to beige and other mica-rich clay minerals. y Invertebrates, Although many shales (p.313) contain more than vertebrates, plants 50 percent silt, siltstones are usually chemically cemented and show cross-bedding, ripple marks, and internal VARIANT layering. This indistinct layering tends to weather at oblique angles unrelated to bedding. Siltstone is Fossiliferous siltstone less common than shale or sandstone and rarely A fern fossil enclosed forms thick deposits. in siltstone

316 ROCKS | SEDIMENTARY ROCKS PROFILE s Detrital, from mud t Marine, freshwater, glacial u Less than ⁄1 256 in (0.1 mm) v Clays, quartz w Calcite x Gray, brown, black y Invertebrates, vertebrates, plants curved fracture mud-sized grain Mudstone specimen MUDSTONE Mudstone is somewhat similar in appearance to siltstone, but A gray or black rock formed from mud, mudstone its grains are smaller and it has a broken surface with a much contains carbon-rich matter, clay minerals, and detrital finer texture. minerals such as quartz (p.168) and feldspar (pp.173–81). VARIANTS Mudstones look like hardened clay and can show the Fossiliferous mudstone A specimen of mudstone with cracks seen in sun-baked clay deposits. numerous invertebrate fossils As in shale (p.313), mudstone’s individual grains are Calcareous mudstone A mudstone variant with a clay- and silt-sized particles that can only be seen under a substantial amount of calcite hand lens. Mudstone generally has the same color range as shale, with similar associations between color and content. Unlike shale, mudstone is not laminated during lithification and is not easily split into thin layers. The lack of layering is either due to the original texture or the disruption of layering. Nautiloid fossil Mudstone deposits may be This fossil nautilus is up to 10 ft (several meters) preserved in mudstone. in thickness. The iridescence of a part of its shell is still visible.

ROCKS | SEDIMENTARY ROCKS 317 PROFILE s Detrital, from muddy sand t Marine u 1⁄256–1⁄16 in (0.1–2 mm) v Quartz, feldspar, mafic minerals w Chlorite, biotite, clay, calcite x Mostly gray or greenish gray; also brown, yellow, or black y Rare poorly sorted minerals fine-grained groundmass Fine-grained graywacke angular fragment This specimen shows the poor sorting characteristic of GRAYWACKE graywacke. The angular clasts are set in a fine-grained matrix. Easily confused with igneous basalt (p.273), graywacke VARIANTS is a turbidite—a rock resulting from rapid deposition in a Dirty sandstone A specimen turbulent marine environment. It gets its name from the from Canada with typical dirty appearance and poor sorting German word grauwacke, which signifies a gray, earthy Turbidite A graywacke formed rock. Also called dirty sandstone, graywacke is hard, by undersea avalanches and mostly gray, brown, yellow, or black. Graywacke is composed of poorly sorted, coarse- to fine- grained quartz (p.168), feldspar (pp.173–81), and dark-colored minerals such as amphibole and pyroxene, set in a fine-grained matrix of clay, calcite (p.114), or quartz. Graywackes may occur in thick or thin beds along with slates (p.293) and limestones (p.319). Graywacke carving In ancient Egypt, this stone was This ancient Egyptian used to make sarcophagi, graywacke carving dates vessels, and statues. from 1370 BCE. It is an offering to the god of writing.

318 ROCKS | SEDIMENTARY ROCKS PROFILE s Detrital t Glacial u From less than ⁄1 256 in (0.1 mm) to many ft (m) v Rock fragments w Rock fragments x Various y None large clast gray clay Tillite specimen matrix The large variation in clast sizes in tillites is evident in VARIANTS this specimen. oversized TILLITE clast Unsorted and unstratified rock material deposited Large clast Tillite with a large by glacial ice that has later been lithified is called tillite. clast in a finer matrix As glaciers move down valleys, they erode and transport rocks. On melting, they deposit this material, which is Differing clast sizes referred to as till. Glacial tills consist of preexisting rock A specimen of tillite with fragments pushed forward or sideways by the glacier, rounded clasts of differing sizes newly eroded material ground or broken up by the glacier, or mixtures of the two. Tillites are typically made of grains with a wide range of sizes. They include fragments ranging from clay-sized particles to large blocks. The largest pieces give rise to the rock’s alternative name, “boulder clay.” The matrix, which frequently comprises a large percentage of the rock, is often made from rock flour, an unweathered and finely ground rock powder. Matching beds of ancient tillites on opposite sides of the South Atlantic Ocean provided early evidence for continental drift—the idea that continents move relative to one another—which was an important precursor to the theory of plate tectonics.

ROCKS | SEDIMENTARY ROCKS 319 Fossiliferous limestone This limestone specimen from Oxfordshire, England, includes several fossil invertebrates. fine texture fossil of shell PROFILE s Chemical, organic t Marine u Crystalline v Calcite w Aragonite, dolomite, siderite, quartz, pyrite x White, gray, pink y Marine and freshwater invertebrates VARIANTS LIMESTONE Coral limestone Limestone Composed mainly of calcite (p.114), this abundant rock formed from fossil coral Freshwater forms multiple layers that are thick and extensive. It can limestone Uncommon be yellow, white, or gray. Specimens can be identified by variant of limestone the rapid release of carbon dioxide and a fizzing sound Oolitic limestone Round when they react with dilute hydrochloric acid. Limestones ooliths set in calcite cement can be compact, grainy, or friable. Many have cross- bedding or ripple marks. The texture of limestone ranges from coarse and fossil-rich to fine and microcrystalline. Limestone generally forms in warm, shallow seas either from calcium carbonate precipitated from seawater or from the shells and skeletons of calcareous marine organisms. It is used in construction, as a raw material Limestone mask in the manufacture of glass, as This face mask dating a flux in metallurgical processes, from the Neolithic Period and in agriculture. has been carved out of mottled limestone.

320 ROCKS | SEDIMENTARY ROCKS PROFILE fine-to-medium texture s Chemical t Marine u Crystalline v Dolomite w Calcite x Gray to yellowish gray y Invertebrates compact carbonate rock Dolomite rock DOLOMITE This specimen of dolomite has a uniform texture that This rock, formed exclusively from the mineral dolomite is typical of the rock. (p.117), is also called dolostone. Most dolomite rocks are VARIANT believed to be limestones (p.319) in which dolomite has Red dolomite A specimen of dolomite colored with iron replaced the calcite (p.114) in contact with magnesium- oxides and hydroxides bearing solutions. This process is called dolomitization. Fresh dolomite looks similar to limestone, while weathered dolomite is yellowish gray. Dolomites have fewer fossils than limestones because fossils and other features are destroyed by the dolomitization process. Dolomite fizzes less violently than limestone when in contact with hydrochloric acid. Dolomite typically occurs as massive layers. It is also present as thin layers or pods within limestone. Dolomite is used as a flux to make steel. It can also Environment-friendly flux be used as a lightweight building In contrast to other steel- aggregate, in breeze blocks, and making fluxes, dolomite in poured concrete. produces slag that can be reused.

Microscopic fossils ROCKS | SEDIMENTARY ROCKS 321 This specimen of chalk, which is almost entirely calcite, is soft, white, made up of tiny fossils of powdery texture marine organisms. fine, white grain PROFILE s Chemical, organic t Marine u Less than ⁄1 256 in (0.1 mm) v Calcite w Quartz, glauconite, clays x White, gray, buff y Invertebrates, vertebrates VARIANTS CHALK Red chalk A specimen of A soft, fine-grained, easily pulverized, white to grayish chalk that takes its color from incorporated hematite variety of limestone is known as chalk. It is composed Marine chalk A specimen of calcite shells of minute marine organisms. Small of chalk pitted by the boring of marine animals amounts of other minerals, such as apatite (p.148), glauconite (p.196), and clay minerals, are usually present. Silica from sponge spines, diatom and radiolarian skeletons, and nodules of chert (p.332) and flint can also be present. Extensive chalk deposits were formed during the Cretaceous Period (142 to 65 million years ago), the name being derived from the Latin word creta, which means “chalk.” Chalk is used to make lime and cement and as a fertilizer. It is also used as a filler, extender, Blackboard chalk or pigment in a wide variety of One of chalk’s longstanding materials, including ceramics uses has been compression and cosmetics. into sticks for writing on blackboards.

322 ROCKS | SEDIMENTARY ROCKS green color Green marl Marls differ in color depending on their mineral content. Green marls, such as this one, are colored by either glauconite or chlorite. fine grain size curved fracture PROFILE MARL s Detrital, from lime mud Calcareous mudstone or marl is a term applied to t Marine, freshwater a variety of rocks that have a range of compositions u Less than ⁄1 256 in (0.1 mm) but are all earthy mixtures of fine-grained minerals. v Clays, calcite In some countries, marl is referred to by the German w Glauconite, hematite terms mergel and seekreide, both of which mean “lake x Various chalk.” Marls usually consist of clay minerals and calcium y Vertebrates, carbonate. They form in shallow freshwater or seawater. The calcium carbonate content is frequently made up invertebrates, plants of shell fragments of marine or freshwater organisms or calcium carbonate precipitated by algae. The high VARIANT carbonate content of marls makes them react with dilute acid. Red marl A specimen colored red by iron oxides Marls are whitish gray or brownish in color but can also be gray, green, red, or variegated. Greensand marls contain the green mineral glauconite (p.196), and red marls, iron oxides. Marl is much less easily split than shale (p.313) and tends to break in blocks. Specimens are often nodular, and the nodules are usually better cemented than the surrounding rock.

PROFILE ROCKS | SEDIMENTARY ROCKS 323 s Evaporite iron-oxide t Marine impurities u Crystalline v Gypsum w Anhydrite x White, pinkish, yellowish, gray y None massive habit ROCK GYPSUM Massive rock gypsum Also called gyprock, rock gypsum is the sedimentary This specimen of rock gypsum is from the Marblaegis mine in rock formed mainly from the mineral gypsum (p.136). Nottinghamshire, England. Although it is commonly granular, it can also occur as VARIANT fibrous bands. Rock gypsum occurs in extensive beds boleite crystal formed by the evaporation of ocean water, in saline lakes, Gypsum with boleite Blue and in salt pans. It also occurs in some shales (p.313), crystals of boleite seen in a matrix of gypsum limestones (p.319), and dolomitic limestones. Rock gypsum is commonly interlayered with other evaporites, such as rock anhydrite (p.133) and salt (p.324). Most of the gypsum that is extracted—about three-quarters of the total production—is calcined (heated to drive off some of its water) for use as plaster of Paris. Unaltered rock gypsum is used as Mesopotamian seal a fluxing agent, fertilizer, filler in This ancient cylinder seal, paper and textiles, and retardant with engravings of stags in Portland cement. and scorpions, is made of alabaster gypsum.

324 ROCKS | SEDIMENTARY ROCKS orange color from iron-rich clays PROFILE crystalline salt s Evaporite Crystalline rock salt t Marine This specimen of crystalline u Crystalline rock salt is colored orange v Halite by iron-rich clays incorporated w Anhydrite during deposition. x White, pinkish, ROCK SALT gray, yellowish Familiar as common table salt, rock salt is the massive y None rock form of the mineral halite (p.110). It occurs in beds VARIANTS that range in thickness from 3 ft (1 m) or so to more than Pink rock salt A specimen colored pink by traces of 990ft (300m). Rock salt forms as a result of the evaporation iron oxides of saline water in partially enclosed basins. It is commonly Massive rock salt Rock salt with coarse, white and interlayered with beds of shale (p.313), limestone (p.319), blue crystals dolomite (p.320), and other evaporites, such as anhydrite (p.133) and gypsum (p.136). Rock salt often occurs in salt domes, which consist of a core of salt surrounded by strata of other rock. The domes can be 1 mile (2 km) or more thick and up to 6 miles (10 km) in diameter. They can occur with petroleum deposits: oil from Natural salt oil-rich shales migrates up and Many people prefer gets caught on the underside natural salt for their cooking. of a salt dome. Much of it comes from evaporating brines.

Porous diatomite ROCKS | SEDIMENTARY ROCKS 325 This specimen of diatomite exhibits its loose, porous typical porous structure structure and rough texture. rough texture PROFILE DIATOMITE s Detrital Also called diatomaceous earth, diatomite consists t Accumulation of of about 90 percent silica; the remainder is made up of compounds such as aluminum oxides and iron oxides. silica-rich organisms Diatomite is easily crumbled into a fine, white to off-white powder. It is made of the fossilized remains of organisms u Less than ⁄1 256 in (0.1 mm) called diatoms. A form of algae, diatoms have hard v Opal shells made of amorphous silica (opal) and containing w None many fine pores. Most float on the surface of the sea. x White Occasionally, large quantities are deposited in ocean y Diatoms sediments, eventually forming diatomite. A few significant deposits of freshwater diatomite are also known. Diatoms are so small that diatomite specimens may contain millions of diatom shells per cubic inch. An important industrial rock, diatomite is easily mined. It is used for the filtration of beverages, liquid chemicals, industrial oils, cooking oils, fuels, and drinking water. Its low-abrasive qualities find use in toothpastes, polishes, and nonabrasive cleaners. It is also used as a filler and extender in paint and paper.

326 ROCKS | SEDIMENTARY ROCKS PROFILE Red-brown laterite sand grains This specimen shows the s Chemical intermixture of iron and aluminum t Postdepositional oxides with sand or other rock u Not granular detritus characteristic of laterites. v Hematite, goethite, iron-oxide calcite, chalcedony minerals w Sand, clay x Red-brown or yellow y None VARIANT LATERITE Desert-varnished laterite Laterite is nodular soil rich in hardened iron and A variant of laterite with a aluminum oxides and resembles bauxite (p.101) in polished surface composition. Nodules of laterite are red-brown or yellow and contain grains of sand or hardened clay. The rock forms in hot, wet tropical climates, where it develops by intensive and prolonged chemical weathering of the underlying rock. Evaporation and leaching of minerals from rock, loose sediment, and soil leaves behind insoluble salts. This results in a variety of laterites, which differ in their thickness, grade, chemistry, and ore mineralogy. Laterite is a source of bauxite, which is an ore of aluminum and exists largely in clay minerals and various hydroxides. Laterite ores have also been a source of iron and nickel. Many laterites are solid enough to be used as building blocks. An example is the laterite seen at the famous temple in Angkor Wat, Cambodia. Crushed laterite has been widely used to make roads. Laterites are also being increasingly used in water treatment.

ROCKS | SEDIMENTARY ROCKS 327 PROFILE oxides and Bog iron nodule hydroxides of iron This nodule of bog iron shows s Chemical varied coloration, which results t Swamps, bogs from the various iron oxides u Less than ⁄1 256 in (0.1 mm) and hydroxides it contains. v Hematite, goethite, calcite, chalcedony w Sand, clay x Light to dark y Plants gray mudstone VARIANT BOG IRON Bog iron ore Gray mudstone Impure iron deposits that develop in bogs or with oxides and hydroxides swamps are known as bog iron. Bog iron is typically of iron a brown-yellow mudstone with yellow, red, brown, or black concretions of iron oxides and hydroxides. In general, bog ores consist of iron hydroxides, primarily goethite (p.102). Bog iron can contain up to 70 percent iron oxide. It often contains carbon-rich plant material, which is sometimes preserved by iron minerals. Bog iron typically forms in areas where iron-bearing groundwater emerges as springs. As the iron encounters the oxygen-rich surface water, it oxidizes, and the iron oxides precipitate out. Bog iron was formerly used as an ore and was widely sought in the preindustrial age. The Romans and the Vikings made extensive use of bog iron as a source of iron. Bog iron was also the principal source of iron in colonial USA. Although it is still forming today, the iron requirements of modern industry demand much larger sources of ore.

328 ROCKS | SEDIMENTARY ROCKS PROFILE s Chemical t Marine, terrestrial u 1⁄256–1⁄16 in (0.1–2 mm) v Hematite, goethite, chamosite, magnetite, siderite, limonite, jasper w Pyrite, pyrrhotite x Red, black, brown, yellow y Invertebrates or plants red color from iron rounded oolith Oolitic ironstone IRONSTONE This specimen of ironstone is made up of small, rounded The term ironstone is applied to sandstones and oolites, which are cemented limestones that contain more than 15 percent iron. by hematite. Ironstones are rich in iron-bearing minerals such as hematite (p.91), goethite (p.102), siderite (p.123), and VARIANT chamosite. These minerals give ironstones a dark red, brown, or yellow color. Sandy ironstone A specimen of a leaf fossil beautifully Ironstone no longer appears to be forming; preserved in ironstone partly because of this, the process by which it forms is something of a mystery. Some ironstones seem to have formed early in Earth’s history when oxygen was not as abundant in the atmosphere as it is now. Precambrian ironstones, which are more than 500 million years old, as well as slightly later ones, formed prior to 240 million years ago, are common. Many of the later ironstones consist of oolites (small spheres) of hematite and contain fossils. Although historically used as an iron ore, ironstone is too limited in quantity to be an economic modern source of iron.

ROCKS | SEDIMENTARY ROCKS 329 Banded ironstone This specimen of ironstone shows prominent banding of alternate chert- and iron-rich material. hematite-rich layer chert layer PROFILE BANDED IRONSTONE s Chemical Also known as banded iron formations, banded t Marine ironstone is made up of thin layers of alternating red, u Neither granular nor brown, or black iron oxides, which may be hematite (p.91) or magnetite (p.92), and gray or off-white shale very fine (p.313) or chert (p.332). It is a very fine-grained rock that breaks into smooth, splintery pieces. Particularly v Siderite, hematite, chert abundant in Precambrian rocks, which are more than w Magnetite, pyrite 500 million years old, banded ironstone can form very x Red, black, gray, striped thick sequences, such as in the Hammersley Range of y None Australia, where it is an economically important iron ore. Banded iron layers are found in some of the oldest known rock formations, dating from more than 3,700 million years ago. These layers are believed to have formed in the seas as a result of dissolved iron combining with oxygen released by the green algae that flourished in the oceans at that time. This was then precipitated into oxygen-poor seafloor sediments that were forming shale and chert. The banding of ironstone is assumed to result from cyclic variations in the oxygen available.

330 ROCKS | SEDIMENTARY ROCKS Calcareous tufa This specimen of calcareous PROFILE tufa is full of holes and irregular shapes. It was formed by the s Chemical evaporation of water. t Terrestrial u Less than 1⁄32 in (1 mm) v Calcite or silica w Aragonite x White y Rare highly porous surface irregular shape VARIANTS TUFA Yellow tufa Irregularly shaped Two different sedimentary rocks that precipitate tufa that lacks bedding from water are known as tufa. Calcareous tufa, or calc- Fossilized tufa Tufa formed around plant remains tufa, is a soft, porous form of limestone deposit composed principally of calcium carbonate (calcite) that precipitates from hot springs, lake water, and groundwater. Calc-tufa is often stained red by the presence of iron oxides. Siliceous tufa, which is also called siliceous sinter, is a deposit of opaline or amorphous silica that forms through the rapid precipitation of fine-grained silica as an encrustation around hot springs and geysers. It is believed to have been partly formed by the action of algae in the heated water. The term “sinter” means that it has several hollow tubes and cavities Stone Wedding in its structure, which are often a This pink tufa formation is result of organic matter that has in the Rhodope Mountains, decomposed later. Bulgaria. It is locally called the Stone Wedding.

ROCKS | SEDIMENTARY ROCKS 331 PROFILE Flint nodule This nodule shows a variation s Chemical in color due to differences in the t Post-depositional extraneous material enclosed u Fine while the silica making the v Pyrite, marcasite rock solidified. w Silica x Various compact silica y Occasional plants and animals sharp edge conchoidal fracture VARIANTS NODULES Melanterite A nodule of A rounded mineral accretion that differs in hydrous iron sulfate composition from its surrounding rock is known as a nodule. Nodules are commonly elongated with a knobby Pyrite nodule A nodule of irregular surface and are usually oriented parallel to the radiating pyrite crystals bedding of their enclosing sediment. Most nodules are formed by the accumulation of silica in sediments and its Marine nodule A nodule subsequent solidification. Nodules containing manganese, of manganese oxides phosphorous, titanium, chromium, and other valuable metals develop on the seafloor but are uneconomical to mine. Other nodules form around plant and animal remains as part of the fossilization process. Pyrite (p.62) is commonly found as nodules. It occurs as spheres, rounded cylinders of radiating crystals, and flat, radiating disks, or “suns.” Clay ironstone, a mixture of siderite (p.123) and clay, sometimes occurs as layers of dark gray-to-brown nodules overlying coal seams. Chert (p.332) and flint often occur as nodules of nearly pure cryptocrystalline quartz (p.168) within beds of limestone (p.319) or chalk (p.321).

332 ROCKS | SEDIMENTARY ROCKS PROFILE Grainy chert This specimen of fine-grained chert s Chemical shows the way the rock breaks t Postdepositional along flat to rounded surfaces. u Not granular v Chalcedony w None x Gray, brown y Invertebrates, plants rounded fracture fine-grained texture surface CHERT VARIANT A rock composed of microcrystalline silica is known Fossiliferous chert as chert. It is commonly gray, white, brown, or black and A specimen containing may contain small fossils. Traces of iron (p.39) may give fossilized primitive chert a light green to rusty-red color. Chert occurs as plants beds or nodules. It breaks along flat to rounded, smooth surfaces and has a glassy appearance. The rock forms by precipitation from silica-rich fluids and colloids. Flint is chert that occurs in marly limestones (p.319) or chalk (p.321). It is generally gray in color. Flint is found as nodules, often in bands parallel to the bedding planes, and breaks with a conchoidal fracture. The nodules are irregular but rounded. Flint resists weathering, so it can form Flint ax thick pebble beds on beaches A prized material for tool and accumulate in soils that are making, flint was one of the derived from chalk. earliest rocks to be mined and extracted.

ROCKS | SEDIMENTARY ROCKS 333 PROFILE pale calcite in crack dark calcareous material s Chemical t Postdepositional u Crystalline v Calcite, silica w Celestine x Gray, brown y Invertebrates, plants Septarian concretion This concretion formed when crystals deposited from percolating brines filled cracks that formed inside a nodule as it shrank. VARIANT CONCRETIONS Ironstone Nodules and concretions are distinctly different concretion geologically, although they have some visual similarities. Pteridosperm Unlike nodules, which are of different compositions than (seed fern) their hosts, concretions are made of the same material fossilized in as their host sediment and cemented by other minerals, an ironstone mainly calcite (p.114), iron oxides, and silica. Concretions are concretion often much harder and more resistant to erosion than their surrounding rock and can be concentrated by weathering. They usually form early in the burial history of the sediment before the rest of the sediment is hardened into rock. Concretions vary in shape, hardness, and size. They can be so small that they need to be seen under a magnifying lens. Specimens can also be huge bodies 93⁄4 ft (3 m) or more in diameter and weighing several tons. In some localities, fossil collectors seek out concretions that have formed around plant and animal remains and perfectly fossilized them. The largest fossil from concretions was an almost complete hadrosaur—a type of dinosaur.

334 ROCKS | METEORITES METEORITES Meteorites are rocks that formed elsewhere in our Solar System and orbited the Sun before colliding with Earth and falling to its surface. The fragments most likely to survive are either very large (weighing 1⁄3 oz/10g or more) or very small (1mg or less). STRUCTURE OCCURRENCE There are three basic types of meteorite: Meteorites are found on every continent. irons, composed mostly of metallic iron They are often found in environments and varying amounts of nickel; stony-irons, where they are highly visible—ice caps and composed of a mixture of iron and silicate deserts being examples. They range in size minerals; and stony meteorites, which from microscopic specimens to masses are further classified into chondrites and that weigh many tons. Rocks that have achondrites, depending on the presence been melted by meteorite impacts called or absence of small igneous, silicate tektites, are also widespread. spheres called chondrules. The most common type of stony-irons are pallasites, THE ORIGIN OF THE SOLAR SYSTEM which are iron meteorites with centimetre- Meteorites are of particular interest in the sized, translucent, olivine or pyroxene study of the origin of the Solar System. crystals scattered throughout. Nearly all meteorites are thought to be fragments of asteroids—rocky bodies that Pallasite section formed in the solar nebula at about the The stony-iron meteorites same time as Earth. Radiometric dating known as pallasites are usually puts the age of most meteorites at about one part olivine crystals to two 4.5 billion years, the same age as Earth. parts metal. In this specimen, olivine is more abundant. Lunar discoveries Over 100 meteorites small to iron-nickel are now believed medium matrix to be material dislodged from the grains olivine crystal Moon, providing a more representative Achondrite sample of the lunar This stony meteorite found surface than those in Haryana, India, lacks brought back chondrules, the small spheres by astronauts. of igneous minerals that would make it a chondrite. Barringer Crater This well-preserved impact crater is in the Arizona Desert, USA, and is 3⁄4 mile (1.2km) in diameter. The meteorite that created it fell about 50,000 years ago and was about 165 ft (50 m) across.

PROFILE ROCKS | METEORITES 335 u Small Iron meteorite v Iron, nickel The kamacite and taenite crystals w Olivine, pyroxene, in this iron meteorite occur as fine, crosshatched lines, forming what is graphite known as a Widmanstätten pattern. x Steel gray on fresh black fusion crust surfaces, black on the outside Widmanstätten pattern nickel-iron crystals VARIANT pointed IRON METEORITE metal These meteorites are believed to be the shattered Fusion surface An iron fragments of the formerly molten cores of large, ancient meteorite with a partially asteroids. As the name suggests, iron meteorites are vaporized surface composed mostly of metallic iron (p.39) and up to 25 percent nickel, to produce two minerals, kamacite and taenite, which are otherwise rare on Earth. Other minerals present in minor amounts in iron meteorites include troilite, graphite (p.46), phosphides, and some silicates—most commonly olivine (p.232) and pyroxene. Iron meteorites are divided into a number of subgroups based on their chemical makeup. Since iron meteorites are so different from most terrestrial rocks, they are recognized more often than other kinds of meteorites and tend to be over represented in meteorite collections. It is estimated that only about 6 percent of meteorites are iron meteorites. Chemical and isotope analysis of a number of iron meteorites indicates that at least 50 distinct parent asteroids were involved in their creation.

336 ROCKS | METEORITES nickel-iron Stony-iron meteorite This sliced specimen of a stony-iron meteorite has areas of nickel-iron and olivine. PROFILE olivine crystal u Small to medium STONY-IRON v Iron, nickel, METEORITE olivine, pyroxene, Composed of a mixture of metallic nickel-iron and plagioclase silicate minerals, stony-iron meteorites make up about 1 percent of recovered meteorites. Pallasites, the most w Various common type of stony-iron meteorites, are iron meteorites x Buff to black on inside, with inch-sized, translucent crystals of olivine (p.232), or sometimes pyroxene, scattered throughout. Pallasites brown to black on were believed to have originated along the boundaries of outside the iron cores and silicate mantles of large asteroids. But some experts now believe they are impact-generated VARIANTS mixtures of core and mantle materials. Meteorite from Antarctica The other main group of stony-iron meteorites are Stony-iron meteorite from the known as the mesosiderites. Relatively rare, these Thiel Mountains, Antarctica consist of about equal parts of metallic nickel-iron and silicate minerals, namely pyroxene, olivine, and calcium- “Thumbprint” surface rich feldspar (pp.173–81). They have an irregular, often Meteorite from Chile with a brecciated texture, with the silicates and metal occurring as melted surface resembling lumps, pebbles, or fine-grained intergrowths. a thumbprint

PROFILE ROCKS | METEORITES 337 u Small to medium black fusion crust v Olivine, pyroxene, thumb-shaped depression plagioclase w Various x Buff to black on inside, brown to black on outside stony interior Stony meteorite The stony composition of this meteorite is visible on its broken surface. Its outside has melted on its passage through the atmosphere. VARIANTS STONY METEORITE Achondrite A specimen with These meteorites can be divided into chondrites and more varied composition achondrites, which are named after chondrules—small, than chondrites igneous, silicate spheres that dominate most chondritic meteorites. Chondrules are largely made up of pyroxene Chondrite Variant of stony and olivine (p.232), with lesser amounts of glass, and may meteorites usually composed contain calcium-rich feldspar (pp.173–81). They can be up to of olivine and pyroxene 3⁄8in (1cm) wide. Chondritic asteroids are some of the oldest and most primitive astronomical bodies in the Solar System. They may have formed by rapid heating in the cloud of dust from which the Solar System originated. More than 80 percent of the meteorites that fall to Earth are chondrites. Achondritic meteorites, in which chondrules are absent, are believed to represent the crust or mantle of asteroids that developed separate mineral shells around an iron-nickel core. They are similar to igneous rocks (pp.258–85) and impact breccias on Earth. Although most achondrites appear to come from asteroids, about 20 of those recovered are believed to have originated on Mars and another 20 on the Moon.

338 GLOSSARY GLOSSARY ACCESSORY MINERAL BASAL CLEAVAGE CLAY A mineral that occurs in a Cleavage that occurs parallel Mineral particles smaller than rock in such small amounts to the basal crystal plane of a about 0.00008 in (0.002 mm). that it is disregarded in mineral. See also cleavage. the definition of the rock. CLEAVAGE BATHOLITH The way certain minerals break ACICULAR HABIT A huge, irregularly shaped along planes dictated by their A needlelike crystal habit of mass of igneous rock formed atomic structure. some minerals. See also habit. from the intrusion of magma at depth. See also magma. COLLOID ADAMANTINE LUSTER Any substance that consists A type of bright mineral luster BLADED HABIT of particles substantially similar to that of diamond. See A crystal habit in which wide, larger than atoms or also luster. flat crystals appear similar to molecules but too small knife blades. See also habit. to be visible to the AGGREGATE unaided eye. An accumulation of mineral BOTRYOIDAL HABIT crystals or rock fragments. A mineral habit in which COLOR DISPERSION crystals form globular The separation of white light ALKALINE ROCK aggregates similar to bunches. into its constituent colors. A class of igneous rocks See also aggregate, habit. abundant in potassium- and CONCHOIDAL FRACTURE sodium-rich minerals. BRECCIA A curved or shell-like fracture A sedimentary rock made up in many minerals and some ALTERATION of angular fragments. See also rocks. See also fracture. The chemical, thermal, or igneous breccia. pressure process or processes CONCRETION by which one rock or mineral CABOCHON A rounded, nodular mass is changed into another. A gemstone cut with a domed of rock formed from its upper surface and a flat enclosing rock and commonly ALTERATION PRODUCT or domed under surface; found in beds of sandstone, A new rock or mineral formed gemstones cut in this way shale, or clay. by the alteration of a previous are said to be cut en cabochon. one. See also alteration. See also cut, gem, gemstone. CONTACT TWINNING The phenomenon of ALUM CARAT two or more crystals Any of a group of hydrated A unit of gemstone weight, growing in parallel contact double salts, usually consisting equivalent to 0.007 oz (0.2 g). with each other and sharing of aluminum sulfate, water of Carat (also spelled \"Karat\") is a common face. See also hydration, and the sulfate also a measure of gold purity, twinned crystals. of another element. the number of parts of gold in 24 parts of a gold alloy: 24 kt is CRYPTOCRYSTALLINE HABIT AMYGDALE pure gold; 18 kt is three quarters A mineral habit that is crystalline A secondary in-filling of a void gold. See also gem, gemstone. but very fine-grained. Individual in an igneous rock. Minerals crystallized components that occur as amygdales CHATOYANCY can be seen only under a include quartz, calcite, and The cat's-eye effect shown by microscope. See also habit. the zeolites. some stones cut en cabochon. See also cabochon. CUT ASSOCIATED MINERALS The final shape of a ground Minerals found growing CLAST and polished gem, as in together but not A fragment of rock, especially emerald cut. See also gem, necessarily intergrown. when incorporated into a gemstone, gem cutting. See also intergrowth. sedimentary rock. DENDRITIC HABIT AUREOLE CLASTIC ROCK A type of habit in which The area around an igneous A sedimentary rock composed crystals form branching, intrusion where contact of cemented clasts. See treelike shapes. See metamorphism has occurred. also clast. also habit.

GLOSSARY 339 DETRITAL ROCKS surface or was ejected as GEM, GEMSTONE Sedimentary rocks formed pyroclastic material. See also A cut stone worn in jewelry, essentially of fragments intrusive rock, lava. valued for its color, rarity, and grains derived from texture, or clarity. It may even existing rocks. See also FACES be an unset stone cut for use sedimentary rock. The external flat surfaces that as jewelry. See also cut, rough make up a crystal’s shape. gemstone. DIATOMACEOUS EARTH A sedimentary rock composed FELDSPATHOIDS GEM CUTTING of the siliceous shells of Minerals similar in chemistry The process of shaping a microscopic aquatic plants and structure to the feldspars gemstone by grinding and known as diatoms. but with less silica. polishing. See also cut, gem, gemstone. DIFFRACTION FELSIC ROCK The splitting of light into An igneous rock with more GLASS its component colors. than 65 percent silica and more A solid substance showing no See also x-ray diffraction. than 20 percent quartz. It is crystalline structure—in effect, also known as acidic rock. a very thick liquid. See also DIKE glassy texture. A sheet-shaped igneous FISSILE TEXTURE intrusion that cuts across A rock texture that allows the GLASSY TEXTURE existing rock structures. rock to be split into sheets. The smooth consistency of See also texture. an igneous rock in which DISCOVERY/TYPE LOCALITY glass formed due to rapid The site where a mineral FLOW BANDING solidification. See also was first recognized as a Layering in a rock that glass, texture. new mineral. originated when the rock was in a fluid, molten state. GRANULAR TEXTURE DOUBLE REFRACTION A rock or mineral texture that The splitting of light into two FOLIATION either includes grains or is separate rays as it enters The laminated, parallel in the form of grains. See a stone. orientation or segregation also texture. of minerals. DRUSY COATING GRAPHIC TEXTURE A sheet of numerous, often FOSSIL The surface appearance of well-formed, small crystals Any record of past life some igneous rocks in which covering a mineral. preserved in the crustal rocks. quartz and feldspar have Apart from bones and shells, intergrown to produce an DULL LUSTER fossils can include footprints, effect resembling a written A type of luster in which little excrement, and borings. script. See also texture. or no light is reflected. See also luster. FRACTURE HABIT Mineral breakage that occurs The mode of growth and EARTHY LUSTER at locations other than along appearance of a mineral. A nonreflective mineral luster. cleavage planes. See also The habit of a mineral results See also luster. cleavage. from its molecular structure. EQUANT FUMAROLE HACKLY FRACTURE A mineral habit that refers to a In volcanic regions, an opening A mineral fracture that has crystal that is of equal size in in the ground through which a rough surface with small all directions; a rock composed hot gases are emitted. protuberances, as on a piece of grains of equal size. of broken cast iron. See GARNET also fracture. EUHEDRAL A member of a group of A term describing crystals with silicates with the general HEMIMORPHIC FORM well-formed faces. formula A3B2(SiO4)3 in which A crystalline form with a A can be Ca, Fe2+, Mg, or Mn2+; different facial development EVAPORITE and B can be Al, Cr, Fe3+, Mn3+, at each end. A mineral or rock formed by Si, Ti, V, or Zr. the evaporation of saline water. HOPPER CRYSTAL GEODE A crystal whose incomplete EXTRUSIVE ROCK A hollow, generally rounded growth has created a hopper- A rock formed from lava that nodule lined with crystals. shaped concavity on one or either flowed onto Earth‘s See also nodule. more faces.

340 GLOSSARY HYDROTHERMAL DEPOSIT LAMELLAR HABIT METAMORPHIC ROCK A mineral deposit that is A type of crystal habit in which A rock that has been formed by hot water plates or flakes occur in thin transformed by heat or ejected from deep within layers or scales. See also habit. pressure (or both) into Earth's crust. another rock. LAVA HYDROTHERMAL MINERAL Molten rock that is extruded METEOR A mineral that is derived onto Earth's surface. See A rock from space that from hydrothermal deposition. also magma. completely vaporizes while See also hydrothermal passing through Earth’s deposit. LITHIFICATION atmosphere. The process by which HYDROTHERMAL VEIN unconsolidated sediment METEORITE A rock fracture in which turns to stone. See A rock from space that reaches minerals have been deposited also recrystallization. Earth’s surface. by fluids from deep within Earth’s crust. See also LUSTER MICA hydrothermal deposit, The shine of a mineral caused Any of a group of hydrous pegmatite, vein. by reflected light. potassium or aluminum silicate minerals. These HYPABYSSAL MAFIC ROCK minerals exhibit a two- A term describing minor An igneous rock with 45–55 dimensional sheet- or igneous intrusions at percent silica. Such rocks have layerlike structure. relatively shallow depths less than 10 percent quartz within Earth’s crust. and are rich in iron-magnesium MICROCRYSTALLINE HABIT minerals.They are also known A mineral habit in which IGNEOUS BRECCIA as basic rocks. See also crystals are so minuscule that An igneous rock made up ultramafic rock. they can be detected only of angular fragments. See with the aid of a microscope. also breccia. MAGMA See also habit. Molten rock that may IGNEOUS ROCK crystallize beneath Earth’s MINERAL GROUP A rock that is formed surface or be erupted as lava. Two or more minerals that through the solidification See also lava. share common structural and/ of molten rock. or chemical properties. MAMILLARY HABIT INCLUSION A mineral habit in which MOONSTONE A crystal or fragment of crystals form rounded A gem-quality feldspar another substance within aggregates. See also mineral that exhibits a silvery a crystal or rock. aggregate, habit. or bluish iridescence. Several feldspars, especially some INTERGROWTH MASSIVE plagioclases, are called Two or more minerals A mineral form having no moonstone. that are growing together definite shape. and interpenetrating each NATIVE ELEMENT other. See also associated MATRIX A chemical element that is minerals. A fine-grained rock into found in nature uncombined which or on top of which with other elements. INTERMEDIATE ROCK larger crystals appear to be An igneous rock that is set. It is also known as NODULE intermediate in composition a groundmass. A generally rounded accretion between silica-rich and of sedimentary material that silica-poor rocks. METAL differs from its enclosing A substance that is sedimentary rock. INTRUSIVE ROCK characterized by high electrical A body of igneous rock that and thermal conductivity NONMETAL invades older rock. See also as well as by malleability, An element, such as sulfur, extrusive rock. ductility, and high reflectivity which lacks some or all of of light. the properties of metals. See IRIDESCENCE also metal. The reflection of light from METALLIC LUSTER the internal elements of a A shine similar to the typical OOLITHS stone, yielding a rainbowlike shine of polished metal. See Individual spherical play of colors. also luster. sedimentary grains from which

GLOSSARY 341 oolitic rocks are formed. Most PLUTON to base, the crystal is said to ooliths comprise concentric A mass of igneous (plutonic) be di- or bi-pyramidal. See layers of calcite. rock that has formed beneath also habit. Earth's surface by the ORE solidification of magma. PYROCLASTIC ROCK A rock or mineral from A rock consisting of airborne which a metal can be POLYMORPH material ejected from a profitably extracted. A substance that can exist volcanic vent. in two or more crystalline OXIDATION forms; one crystalline form PYROXENE The process of combining with of such a substance. See A member of a group of oxygen. In minerals, the oxygen also pseudomorph. 21 rock-forming silicate can come from the air or water. minerals that typically form PORPHYRITIC TEXTURE elongate crystals. PEGMATITE An igneous rock texture in A hydrothermal vein composed which large crystals are set RADIOMETRIC DATING of large crystals. See also in a finer matrix. See also The determination of absolute hydrothermal vein. phenocryst, texture. ages of minerals and rocks by measuring certain PENETRATION TWINNING PORPHYROBLAST radioactive and radiogenic The phenomenon of two or A relatively large crystal set atoms in them. more crystals forming from a in a fine-grained matrix in common center and appearing a metamorphic rock. RARE-EARTH MINERAL to penetrate each other. See A mineral containing a also twinned crystals. PORPHYROBLASTIC TEXTURE significant portion of one A texture characterized or more of the 17 rare-earth PHENOCRYST by relatively large crystals elements, principally ytterbium, A large crystal set in an in a fine-grained matrix. See gadolinium, neodymium, igneous rock matrix, creating also texture. praseodymium, cerium, a porphyritic texture. See also lanthanum, yttrium, porphyritic texture. PRECIPITATION and scandium. The condensation of a solid PISOLITIC HABIT from a liquid or gas. RECRYSTALLIZATION A mineral habit characterized The redistribution of by pea-sized grains with a PRIMARY MINERAL components to form concentric inner structure. A mineral that has crystallized new minerals or mineral See also habit. directly from an igneous crystals; in some cases magma and is unaltered new rocks form. It occurs PLACER, PLACER DEPOSIT by rain, groundwater, or during lithification and A deposit of minerals derived other agents. See also metamorphism. See by weathering and secondary mineral. also lithification. concentrated in streams or beaches because of the PRISMATIC HABIT REFRACTIVE INDEX mineral's high specific gravity. A mineral habit in which A measure of the slowing parallel rectangular crystal down and bending of light as PLASTIC ROCK faces form prisms. See it enters a stone. It is used to A type of rock that is easily also habit. identify cut gemstones and folded when subjected to high some minerals. See also cut, temperature and pressure. PROTOLITH gem, gemstone. A rock that existed prior to PLATY HABIT undergoing metamorphic RENIFORM HABIT The growth habit shown by flat, transformation into a different A mineral habit with a thin crystals. See also habit. rock type. kidneylike appearance. See also habit. PLAYA DEPOSIT PSEUDOMORPH A mineral deposit formed A crystal with the outward REPLACEMENT DEPOSIT in a desert basin that is form of another species of A deposit formed from intermittently filled with a lake. mineral. See also polymorph. minerals that have been altered. See also PLEOCHROIC, PLEOCHROISM PYRAMIDAL HABIT alteration product. The phenomenon of a mineral A crystal habit in which or gem presenting different the principal faces join at RESINOUS LUSTER colors to the eye when viewed a point. When two such A shine having the reflectivity from different directions. pyramids are placed base of resin. See also luster.

342 RETICULATED SILICA-RICH ROCKS TERMINATION Having a network or a netlike Rocks containing more than Faces that make up the ends mode of crystallization. 50 percent silica. See also of a crystal. silica-poor rocks. ROCK FLOUR TEXTURE Very fine-grained rock SLATY CLEAVAGE The size, shape, and dust, often the product The tendency of a rock, such relationships between rock of glacial action. as slate, to break along flat grains or crystals. planes into thin, flat sheets. ROUGH GEMSTONE See also cleavage. TWINNED CRYSTALS An uncut gemstone. See also Crystals that grow together as cut, gem, gemstone. SOLID-SOLUTION SERIES mirror images with a common A series of minerals in which face (contact twins) or grow SALT DOME certain chemical components at angles up to 90 degrees A large, intrusive mass of salt, are variable between two to each other and appear to sometimes with petroleum end-members with penetrate each other trapped beneath. fixed composition. (penetration twins). SCHILLER EFFECT SPECIFIC GRAVITY ULTRAMAFIC ROCK The brilliant play of bright The ratio of the mass of a An igneous rock with less than colors in a crystal, which is mineral to the mass of an 45 percent silica. It is also often due to minute, rodlike equal volume of water. Specific known as an ultrabasic rock. inclusions. gravity is numerically See also mafic rock. equivalent to density (mass SCHISTOSITY divided by volume) in grams VEIN A foliation that occurs in per cubic centimeter. A thin, sheetlike mass of coarse-grained metamorphic rock that fills fractures in rocks. It is the result of SPHEROIDAL HABIT other rocks. platy mineral grains. See A crystal habit in which also foliation. numerous crystals radiate VESICLE outwards to form a spherical A small, spherical or oval cavity SCORIACEOUS mass. See also habit. produced by a bubble of gas A term for lava or other or vapor in lava, left after volcanic material that is STALACTITIC HABIT the lava has solidified. See heavily pitted with hollows A mineral habit in which the also lava. and cavities. See also lava. crystalline components are arranged in radiating groups VITREOUS LUSTER SECONDARY MINERAL of diminishing size, giving the A shine resembling that A mineral that replaces appearance of icicles. See of glass. See also luster. another mineral as a also habit. result of weathering or VOLCANIC PIPE alteration. See also alteration, STRIATION A fissure through which lava primary mineral. A parallel groove or line flows. See also lava. appearing on a crystal. SECTILE WELL-SORTED ROCK The property of a mineral that SUBLIMATION, SUBLIMATE A sediment or sedimentary allows it to be cut smoothly The process by which a rock with grains or clasts that with a knife. See also fracture. substance moves directly from are roughly of the same size. a gaseous state to a solid state. SEDIMENTARY ROCK A sublimate is the solid X-RAY DIFFRACTION A rock that either originates product of sublimation. The passing of x-rays through on Earth's surface as an a crystal to determine its accumulation of sediments SUNSTONE internal structure by the or precipitates from water. A gemstone variety of feldspar way in which the x-rays are with minute, platelike scattered. See also diffraction. SEMIMETAL inclusions of iron oxide A metal, such as arsenic or oriented parallel to one ZEOLITE bismuth, that is not malleable. another throughout. See A group of hydrous aluminum See also metal. also gem, gemstone. silicates characterized by their easy and reversible SILICA-POOR ROCKS TABULAR HABIT loss of water. Rocks containing less than A crystal habit in which the 50 percent silica. See also crystals have long, flat, parallel silica-rich rocks. faces. See also habit.

INDEX 343 INDEX antimony sulfide 61 beryl 20, 198, 225, 240 Apache Tears 280 beryllium 225 Page numbers in bold indicate apatite 13, 17, 148 beryllium aluminum oxide 81 main entries. Biot, Jean-Baptiste 197 and other minerals 85, 153–54, biotite 11, 197 A 156, 176 and extrusive igneous rocks a axis, crystals 20, 22–23 and rocks 262, 321 274–75, 278–79 abalone 249 crystal system 22 acanthite 49, 54, 69, 72 aplite 186 and intrusive igneous rocks 258, accessory minerals 10 apophyllite 11, 186, 188, 204 262–64 achondrites 334, 337 appearance, crystal 21 achroite 224 aquamarine 134, 148, 225, 260 and metamorphic rocks 288, acicular crystals 21 aragonite 115, 246–49 291–92, 294 acicular epidote 230 arfvedsomite 262 acids, for cleaning 32–33 argentite 49 and other minerals 181, 199, 233 acmite 209 argentopentlandite 55 and subvolcanic igneous actinolite 90, 213, 217, 219, 220, arkose 311 arsenates 13, 147, 160–165 rocks 270 291, 296 arsenic 41, 45, 58, 59, 72, 73, 151 biotite schist 292 Adam, G.J. 160 in arsenates 147 bismuth 40, 41, 66, 73 adamite 160, 161, 165 native element 36 bitumen 246 Aegir 209 arsenic sulfide 59 bituminous coal 253 aegirine 76, 182, 209, 262 arsenopyrite 83, 148 bixbyite 98 agate 168, 169, 170 asbestos 192 black coral 247 age-dating, radiometric 309, 334 actinolite 220 “black granite” 264, 268 agglomerate 283, 284 anthophyllite 216 black-lip shell 248 aggregates, crystal 21 blue 222 black mica 197 ailsite 222 glaucophane 221 black silver ore 69 alabaster 114 riebeckite 222 bladed crystals 21 albite 76–77, 86, 177, 262 tremolite 219 blastomylonite 289 ash tuff 282 blister pearl 248 in granite 11 asterism effect 78 blocky crystals 21 solid-solution series 167 asteroids 27, 334–35, 337 blue asbestos 222 twinning 19 atacamite 106 blue coral 247 alexandrite 81 atomic structure 18 Blue John 109 alexandrite effect 244 augen gneiss 288 blue labradorite 180 almandine 221, 243 augite 176, 179, 182, 211, 265 blue ocher 157 aluminum 98–99, 101, 108, 326 in gabbro 11 blue porphyry 181 and halides 106 aureole 287 blue vitriol 138 ores 100 autunite 149, 152 bluestone 268 aluminum oxide 74, 95, 101 axinite 23, 228 boart diamond 47 aluminum phosphate 158 axis, crystallographic 20, 22–23 bog iron 102, 327 aluminum silicate 194, 236–37 azurite 10, 14, 113, 120 bohernite 100 amazonite 175 boleite 323 amber 13, 246, 250, 251 B bomb, volcanic 282, 285 amesite 191 bomb tuff 282 amethyst 13, 148, 168, 170 b axis, crystals 23 boracite, crystal structure 126 amphibole 191, 270, 278–79, 317 babbitt metals 41 borates 13, 126, 127–130 amphibolite 180, 218, 231, 296 bags, for collecting 32 borax 126, 127, 129–30 analcime 185, 190 baguette cut 25 Born, Ignaz von 50 anatase 76, 77 banded iron formation 329 bornite 10, 50, 51–52, 67, 73 and other minerals 124–25, 139, banded ironstone 329 barite 11, 61, 66, 73, 103, 116, 134, crystal structure 48 160–62, 203 boron 126–27, 130 andalusite 236, 294 155, 164 bort diamond 47 Andes Mountains 181 cleavage 16 botryoidal habit 21 andesine 167, 181, 264, 275 crystal structure 131 boulder clay 318 andesite 257, 275 barium 94, 113, 116 boulder-conglomerate 306 barium carbonate 116 boulder opal 172 and minerals 180–81, barium sulfate 134 Bournon, Count J.L. de 71 188–89, 207 basalt 257, 273 bournonite 65, 71 and other minerals 96, 180, 204, bradawl, for cleaning 32 and other rocks 274, 278 brain coral 247 andradite 302 207, 211 breadcrust bomb 285 anglesite 54, 119, 132 and other rocks 265–66, breccia 307 anhydrite 67, 128–29, 133, 323–24 Anker, M.J. 122 299, 317 marble 301 ankerite 122 zeolites 186–90 volcanic 283, 284 annabergite 163 batholith 256 Breithaupt, August 178 annivite 73 battery, lithium 198 brilliant cut, diamond 25 anorthite 167, 179 bauxite 97, 100, 101, 104, 194, 326 brittle minerals 16 anorthoclase 167, 176 beaches, collecting on 28–29 brittle silver ore 69 anorthosite 179, 261 bentonite 200 Brochant de Villiers, A.J.M. 139 anthophyllite 216, 300 Bergmann, Torbern Olaf 152 brochantite 139, 161–62 anthracite 253 bromine 106 antigorite 191 bronze 37 antimony 41, 45, 61, 65, 68, 71, 73

344 INDEX Brooke, H.J. 77 cerussite 54, 113, 119, 124, cobalt 45, 55 brookite 76, 77 143, 15 1 cobalt arsenate hydrate 163 brown topaz 234 cobalt bloom 163 brown zircon 233 twinning 19 cobaltpentlandite 55 Bruce, Archibald 105 cesium 198, 270, 272 cobble-congolmerate 306 brucite 13, 105, 298 chabazite 189 cockscomb barite 134 “Bruneau jasper” 171 chalcanthite 137, 138 cogwheel ore 65, 71 brushes, for cleaning 31–33 chalcedony 168, 169, 170, 203 Coleman, William 130 butterfly spar 114 chalcocite 50, 51, 52 colemanite 126, 128, 130 bytownite 167, 261 chalcophyllite 162 collecting rocks and minerals chalcopyrite 57, 138 C 28–29 and sulfide minerals 50–52, code 29 c axis, crystals 20, 22–23 54–55 equipment 30–31 calamine 227 color of minerals 14 calc-tufa 330 and sulfosalt minerals 66–67, coltan series 82 calcareous tufa 330 71, 73 columbite 84 calcite 9, 11, 17, 114 columbite-tantalite 82 fracture 16 comet Wild 2 179 and other minerals 88, 103, 112, streak 15 common mica 195 115, 121, 141, 249 chalcosine 13, 51 compass, magnetic 29 chalcotrichite 87 conch 249 and other rocks 269, 272, 296, chalk 63, 196, 321, 331–32 conchiolin 247 301–02 chalybite 123 conchoidal fracture 16 chamosite 328 concretion 333 and sedimentary rocks 309–10, chatoyancy 81 conglomerate 83, 306 313, 316–17, 319–21, 330, 333 chemical elements, table of 12 contact metamorphism 287 chemical sedimentary rocks 305 continental drift 318 and silicate minerals 183, 186, chert 321, 329, 331, 332 copal 246, 250, 251 190, 193, 205, 229 as sedimentary rock 305 copalite 251 chessylite 120 copper 37 and sulfur minerals 51, 58, 68, chiastolite 236, 303 and other minerals 40, 43, 48, 74, 70, 72 chiastolite slate 293 “chimney,” seafloor 117, 120, 125 as a carbonate 113 and rocks 302 as a cementing agent 304 hydrothermal 133 and sulfur minerals 50–52, 54, as an organic mineral 246 chisels, for collecting 30 crystal structure 113 chlorapatite 148 57, 60, 67, 73, 137–139 fluorescence 17 chlorine 106 ductile 16 luster 15 chlorite, native element 8, 10, 13, 36 refraction 17 copper aluminum phosphate 154 calcium 89 and other minerals 38, 89, copper aluminum silicate 203 calcium aluminum silicate 205, 105, 221 copper arsenic sulfide 67 copper carbonate 120 231, 245 and rocks 289, 291–92, 294, 300, copper glace 51 calcium aluminosilicate 179 315, 322 copper iron arsenic sulfide 66 calcium bentonite 200 copper iron sulfide 50, 57 calcium borosilicate hydroxide 129 chlorite schist 118 copper oxide 87 calcium carbonate 114, 122, chocolate 201 copper sulfate hydrate 138–39 chondrites 334, 337 copper sulfide 52, 161 247, 249 chondrules 334, 337 coral 246, 247, 319 calcium magnesium silicate chromates 13, 131, 142 Cordier, Pierre L.A. 223 chrome diopside 210, 269 cordierite 223, 236–37, 217, 219 chrome yellow 142 calcium phosphate 148 chromite 74, 96, 99 294, 303 calcium sulfate hydrate 136 chromium 74 correction fluid, for labeling 29 calcium sulfite 133 corundum 17, 74, 81, 95, 104, calcium titanium oxide 89 and minerals 96, 99, 104, 142 calcium titanium silicate 235 and rocks 265–66, 270, 331 236–37 calcium tungstate 146 in chromates 131 corundum schist 292 calcium uranium phosphate 149 in emerald 225 cotton stones 188 calomel 112 chrysoberyl 81 Covelli, Niccolo 52 campylite 164 chrysocolla 10, 125, 203, 226 covellite 51, 52, 67 carbon 36, 46–47 chrysoprase 169 Cretaceous Period 321 carbonado 47 chrysotile 191, 192 crocidolite 222 carbonate cycle 246 cinnabar 56, 61, 112 crocoite 15, 142 carbonates 8, 9, 13, 113, cinnamon stone 245 cryolite 106, 108 citrine 168 cryptocrystalline quartz 331 114–125, 313 clams 248 crystal axes 20, 22–23 carbonatite 117, 122, 272, 284 clastic sedimentary rocks 304–05 crystals 18–23 Carnall, Rudolf von 107 clay 63, 101, 123, 134, 171, 202, 313 carnallite 106, 107 boulder 318 aggregates 21 carnelian 24, 169 clay-based minerals 200–206 appearance 21 Carno, Marie-Adolphe 159 clay ironstone 331 axes 20, 22–23 carnotite 147, 152, 159 cleaning specimens 32–33 cubic 19, 20, 22 cassiterite 74, 79, 83, 241 cleavage 16 faces 20 cat’s eye chrysoberyl 81 cleavelandite 173, 177 forms 20 catalytic converters 223 clinochrysotile 192 habits 18, 20–21 caustic potash 107 clinoclase 161, 162 hexagonal 22 celestine 13, 135 clothing, for collecting 31 monoclinic 23 cementing in sedimentary coal 253 orthorhomic 23 and minerals 60, 62–63, 123, 137, rocks 304 cerium 74, 89, 93 140, 246, 251–52 cerium oxide 150 as a hydrocarbon 12 cerium phosphate 150

INDEX 345 crystals continued ductile minerals 16 “fishtail” gypsum 19, 136 structure 18 dynamic metamorphism 286 flexible minerals 16 symmetry 19 dysprosium 93 flint 321, 331, 332 systems 19, 22–23 flos ferri 115 tetragonal 22 E flour, rock 318 triclinic 23 flow banding 278, 280 trigonal 22 earth, diatomaceous 325 fluorapophyllite 204 twinning 19 eclogite 299 fluorescence 17 elastic minerals 16 fluoridated manganese cubic crystals 20, 22 elbaite 224 cuprite 74, 87, 162 electrical charge 9 phosphate 153 Curie, Pierre and Marie 83 elements, fluorine 106 curling 222 fluorite 17, 64, 66, 76, 109, 121 cushion cut 25 native 36 cuts, gems 25 table of 12 color range 14 cuttlefish 206 trace 14 crystal structure 106 cycle, rock 27 emerald 12, 225, 226 fluorspar 109 cyclic twinning 19 enargite 67 fool’s gold 62 cyclosilicates 166, 223–26 enstatite 208 formanite-(Y) 93 cyprine 229 epidote 214, 221, 230, 296 forsterite 10, 193, 232 epsom salts 140 fortification agate 170 D epsomite 140 fossils 63, 310, 313, 315–16, 319, equant crystals 21 dacite 263, 274, 283 equipment, for collecting 30–31 321, 325, 328, 330, 332–33 dark ruby silver 70 erbium 93 sedimentary rock 305 de Bournon, Count J.L. 71 erythrite 163 fracture 16 de Dolomieu, Déodat Gratet 117 essential minerals 10 franklinite 88, 96 de Villiers, A.J.M. Brochant 139 euclase 240 frost 75 denarius coins 70 eucryptite 212 fuchsite 195, 221 dendritic crystals 21 eudialyte 262 fumaroles 8, 36, 44, 133, 141 deposition 304 extrusive igneous rocks 26–27, Funerary Temple 202 desert rose barite 134 desert rose gypsum 136 257, 273–79 G diabase 190 eye shadow 183 diamond 17, 47 gabbro 90, 180, 261, 265, F 267–68, 296 and other minerals 36, 46, 81, 90, 95, 99, 201, 233–35, 243 faces, crystal 20, 22–23 Gahn, John Gottlieb 97 faceting, gems 25 gahnite 96, 97 and rocks 269–70, 299, 306 facies, grabulite 297 galena 11, 54 faceting 25 fayalite 232 mining 24 and carbonates 116, 119, 121 synthetic 12 solid solution 10 and phosphates 151, 155 diaspore, crystal structure 100 feldspar porphyry 271 and sulfur minerals 49, 51, 53, diatomaceous earth 325 feldspars 9, 93, 173–181 diatomite 325 61, 65, 67, 70–73, 132 diatoms 325 and igneous rocks 258–60, 262, luster 15 dickite 201 275, 278, 280 garlic odor 59 dike 256 garnet 11, 242–45 dinosaurs 333 and metamorphic rocks 288, and minerals 42, 84, 147, 214 diopside 210 290–91, 293–94, 296 and rocks 261, 267, 269, 288, and other minerals 209, 211, 214, and minerals 202, 233 291, 296–97, 299, 302 219, 229, 245 and sedimentary rocks 310, 313, pyrope 266 and rocks 297, 299, 302 solid-solution series 166 dioptase 226 316–17, 336–37 garnet-chlorite schist 292 diorite 90, 178, 180–81, 263, plagioclase 261, 264 garnet hornfels 303 series 167 garnet schist 292 264, 275 twinning 19 gas, natural 12 dirty sandstone 317 feldspathoids 182–184, 270 gelane 66 diaspore 104 felsic rocks 257 gems 24–25 displaying specimens 33 Ferber, Moritz Rudolph 145 Genesis Rock 179 dodecahedral crystal form 20 ferberite 64, 79, 145 gibbsite 100 dogtooth spar 114 Ferguson, Robert 93 glacial till 318 dolerite 186, 207, 268 fergusonite 93 glaciers 75 Dolomieu, Déodat Gratet de 117 ferroactinolite 219, 220 glass 337 dolomite, ferroanthophyllite 216 muscovy 195 ferroaxinite 228 volcanic 277–78, 280–81 and other minerals 54, 60, ferrocolumbite 82 Glauber, Johann 141 68, 122, 140, 184, 210, 217, 241 ferroglaucophane 221 Glauber’s salt 141 ferrohornblende 218 glauberite 128, 141, 172 and rocks 272, 284, 301–02, ferrosilite 208 glauconite 196, 309, 314, 324 fertilizers 147, 185 fibrous habit 21 321–22 as a carbonate 113 field equipment, collecting glaucophane 221, 291 as a mineral 117 gloves, for collecting 30 as a rock 320 30–31 gneiss 288 occurrence 9 field techniques, collecting dolomitization 320 and feldspars 173, 175, 178 dolostone 320 28–29 and nesosilicates 235, double refraction 17 fingernail test 17 “dragon’s blood” 56 fire agate 170 238–39, 243 dravite 224 fire opal 172 and other minerals 61, 76, fireworks 126 78, 81, 97, 150 and other rocks 290, 297, 310

346 INDEX gneiss continued hausmannite 98 iron hat 102 and other silicates 186, 190, 195, haüyne 183 iron magnesium silicate 241 197, 216, 218, 223, 231 heavy spar 134 iron mica 197 as metamorphic rock 286–87 hedenbergite 209, 211 iron oxide 92, 102, 326 heliodor 225 iron roses 91 Goethe, Johann Wolfgang von 102 hematite 91 iron sulfate hydrate 137 goethite 100, 102 iron sulfide 8, 63 and other minerals 38, 78, 87, 90, iron tungstate 145 and halides 107, 112 92, 101, 107, 110, 171, 241 ironstone 92, 122, 172, 328 and other minerals 87, 103, 120, and rocks 280, 313, 321, 328–29 banded 329 151, 155, 158, 161, 165, 171 luster 15 clay 331 and rocks 313, 327–28 streak 15 concretion 333 goggles, for collecting 30 hemimorphic crystal form 20 isinglass 195 gold 42, 48, 146, 201, 272, 302 hemimorphite 124, 160, 227 isometric crystal system 22 crystals 36 hessonite 245 fracture 16 Heuland, J.H. 187 J malleable 16 heulandite 186, 187, 188 native element 8, 13, 36 hexagonal crystal system 22 jack-straw cerussite 119 goshenite 225 hiddenite 212 jade 213 gossan 102 history, gems 24 granite 258 Hope diamond 47 nephrite 219–20 and cyclosilicates 223, 225 horn mercury 112 jadeite 167, 213, 221 and feldspar minerals 173, horn quicksilver 112 Jameson, Robert 68 hornblende 218 jamesonite 68 175, 178 and igneous rocks 262–64, 270 jasper 168, 171 and nesosilicates 234, 236, 244 and metamorphic rocks 288, jet 252 and other minerals 61, 64, 78, 97, 291, 296 K 108, 150, 158, 222 and other minerals 181 and other rocks 260, 262, 264, hornblende granite 258 kamacite 39, 335 hornfels 237, 303 kaolinite 138, 201 270, 288, 290, 302, 310 pyroxene 267 kauri gum 250 and phyllosilicates 195, 197, 201, How, Henry 129 kernite 126, 129 howlite 129 kerogen 314 204–05 Hübner, Adolf 144 Khalkedon 169 and zeolites 186–87, 189–90 hübnerite 144, 145 kidney ore 91 “black” 264, 268 Hume, Sir Abraham 241 Kimberley 269 graphic 259 humite 241 kimberlite 24, 47, 90, 96, 210, hornblende 258 hydrocarbons 12 metamorphism 287 hydroxides 13, 100, 101–05 266, 269 orbicular 259 hydroxyapophyllite 204 Klaproth, M.H. 83 porphyritic 259 hydroxyl radical 100, 148 knives, for collecting 31 textured 259 hypabyssal intrusive rocks 256 Krakatoa 277 granodiorite 175, 263, 264, 270, hypersthene 297 kunzite 212 kyanite 236, 238, 291, 295 274, 288 I kyanite schist 291–92 granulite 229, 243, 297 graphic granite 259 ice 12, 75 L graphite 13, 46, 64 idiocrase 229 igneous rocks 26–27, 256–57 labeling specimens 33 and rocks 291–94, 301, 335 labradorite 167, 180, 261 green apophyllite 204 extrusive 26–27, 257, 273–79 laccoliths 256 greensand 196, 309 intrusive 26–27, 256, 258–67 lamellar crystals 21 greensand marl 322 sub-volcanic 268–72 Lamma, Statue of 162 graywacke 296, 308, 317 volcanic 257, 280–85 lamproite 47 grinding, gems 25 ignimbrite 282 lamprophyre 270 gritstone 312 illite 202 lanthanum 93, 150 grossular 229, 245 ilmenite 76, 90, 176, 265, 269 lanthanum phosphate 150 grossular garnet 214 imperial jade 213 lapilli 285 gyprock 323 imperial topaz 234 lapilli tuff 282 gypsum 17 Indian pearl 248 lapis lazuli 183, 184 indicolite 224 larvikite 176 and other minerals 111, 133, 141 inosilicates 166, 207–22 laterite 104, 326 and other rocks 324 intermediate rocks 257 lattice, crystal 18 mineral 131, 136 intrusive igneous rocks 26–27, 256, lava 257 rock 323 layered gabbro 265 258–67 lazurite 183 H iodine 106 lead, iolite 223 habit, crystal 18, 20–21 iridium 38 and native elements 40, 41, 43 hackly fracture 16 iron 36, 39 and other minerals 113, 117, 119, hafnium 272 hailstones 75 and meteorites 334, 335, 336–37 132, 134, 142, 151 hair, Pele’s 281 and other minerals 55, 62, 101, and rocks 302 halides 13, 106, 107–12 and sulfide minerals 53–54, 64 halite 106, 110, 111, 127, 133, 324 109, 122, 123, 137 “lead,” pencil 46 and oxide minerals 77, 91, 92, lead chloro vanadate 155 cubic crystal 19 lead copper antimony sulfide 71 halloysite 201 98–99 lead iron antimony sulfide 68 halogens 106 and rocks 265, 270, 302 hammers, for collecting 30 bog 327 hardness 17 iron chromium oxide 99 hats, for collecting 30 Hausmann, Johann Friedrich Ludwig 98

INDEX 347 lead sulfide 54 manganite 103, 104 molybdate 13, 131, 143 lenses, for collecting 31 maps, for collecting 29 native element 8, 13, 36, 37–47 lepidolite 86, 198, 212 marble 272, 301 organic 13, 246, 247–53 Les-Beaux-De-Provence oxide 8, 9, 13, 74, 75–99 and minerals 81, 104–05, 114, phosphate 13, 147, 148–58 (bauxite) 100 117, 148, 183, 229, 235 primary 10 leucite 185 refractive index 16 leucogabbro 265 quarrying 26 secondary 10 liddicoacite 224 marcasite 8, 18, 63 silicate 9, 13, 166–67, 168–245 light red silver ore 72 streak 15 lignite 251, 253 and other minerals 48, 50, 56, sulfate 131–41 lilac jadeite 213 91, 137 sulfide 13, 48, 49–64, 74 limestone 305, 319 sulfosalt 65, 66–73 maria (lunar \"seas\") 207, 273 tenacity 16 and carbonate minerals 114, marl 62, 314, 322 tungstate 13, 131, 144–46 117–18, 122 marquise cut 25 vanadate 13, 147, 159 Mars 273, 337 mines 24, 28–29 and metamorphic rocks 301, 302 massive habit 21 mixed cut 25 and other minerals 60, 63, 96–97 Medusa 247 Mohs scale 17 and sedimentary rocks 313–14, meerschaum 206 molluscs 248–49 melanterite 137, 331 molybdates 13, 131, 143 317, 320, 323–24, 331–32 mercury 56, 65–66, 112 molybdenite 64, 79, 143 and silicate minerals 184, 196, molybdenum 64, 131, 143, 302 horn 112 molybdenum sulfide 64 210, 214, 224, 229, 241 mercury chloride 112 monazite 84, 150 limestone breccia 307 mercury sulfide 56 monoclinic crystal system 23 limonite 100, 151, 160 mesolite 188 Mont St.-Hilaire 184 lipstick 194 mesosiderite 336 Moon, lithification 304 meta-autunite 149 anorthosite 261 lithium 86, 97, 198, 212 metamorphic rocks 26–27, basalt 273 lizardite 191 meteorites 334, 337 lodestone 92 286–87, 288–303 minerals 39, 53, 179, 207, 211 lunar rocks see Moon metaquartzite 310, 295 rocks 39, 53, 207 luster 15 metatorbernite 152 silicates 167 meteorites 27, 55, 334 moonstone 173, 176 M morganite 225 and minerals 53, 60, 89, 118, 179, mother of pearl 115, 248–49 maceral 253 207, 208, 211, 245 Mount Fujiyama 275 mafic rocks 257 Mount Saint Helens 257, 274 magma 26–27, 48, 256–57 and native elements 36, 39 Mount Vesuvius 184, 229 magnahumite 241 and silicates 167 mudstone 288, 291, 293–94, 315, magnesia, medical 105 iron 335 magnesioanthophyllite 216 stony 337 316, 327 magnesioaxinite 228 stony-iron 336 calcareous 322 magnesiohornblende 218 mica schist 81, 239 mullite 238 magnesite 118, 206 micaceous hematite 91 muscovite 148, 195, 202, 258, magnesium 98–99, 107, 118, micas 11, 195–99, 201, 202 and igneous rocks 258, 263, 260, 292 122, 270 muscovite mica 294 magnesium carbonate 118 269, 278 muscovite schist 291–92 magnesium hydroxide 105 and metamorphic rocks 289, muscovy glass 195 magnesium silicate 191 mylonite 289 magnesium sulfate 140 291, 293, 295, 301 magnetite 92 and sedimentary rocks 308, 315 N microcline 167, 175, 176, 262 and igneous rocks 262, 265, 267, microlite 86 nacrite 201 269, 272 micromounts 31 nailhead spar 114 microscope, for collecting 31 native elements 8, 13, 36, 37–47 and other minerals 85, 90, migmatite 290 natrolite 185, 186, 188 102, 181 milky quartz 168 natural gas 12 Miller, W.H. 60 nautilus 316 and other rocks 298, 310, 329 millerite 60 nemalite 105 in gabbro 11 Millstone Grit 312 neodymium 93, 150 streak 15 mimetite 151, 155, 160, 164 neodymium phosphate 150 magnifiers, for collecting 31 minerals 8–17, 34–253 nesosilicates 166, 232–45 malachite 10, 125 accessory 10 nepheline 182, 185, 267 and other minerals 113, 124, 139, arsenate 13, 147, 160–65 nepheline syenite 262 associations 10–11 nephrite 213, 217 161, 162, 203 borate 13, 126, 127–30 nephrite jade 219–20 malleable minerals 16 carbonate 8–9, 13, 113, nickel, mamillary jasper 171 manganaxinite 228 114–125, 313 and igneous rocks 265–66, manganese, chromate 13, 131, 142 270, 272 classification 12–13 and hydroxide minerals cleavage 16 and meteorites 334–37 102–03, 105 color 12 and minerals 39, 45, 55, 60, 85 composition 8–9 and sedimentary rocks 326 and other minerals 80, 94, 98, essential 10 nickel iron sulfide 55 113, 122, 144–45 fluorescence 17 nickel sulfide 60 fracture 15 and oxide minerals 74, 80, groups 10–11 94, 98 halide 13, 106, 107–12 hardness 16 and rocks 331 hydroxide 13, 100, 101–05 and silicate minerals 215–16 identification 14–15, 16–17 manganese aluminum silicate 244 luster 15 manganese bronze 80 manganese carbonate 121 manganese oxide 94, 103

348 INDEX niobates 82 and other minerals 40, 64, Prehn, Hendrik von 205 niobium 77, 82, 84–85, 89, 93, 272 108, 123 prehnite 141, 190, 205 niobium sodium calcium oxide 85 primary minerals 10 nitrates 13 and oxide minerals 81, 82, 84–86, prism face 20 nodule 331, 333 90, 93, 95, 97 Prontium copal 250 note-taking, for collections 29 protective equipment, for and phosphate minerals 149, O 150, 153, 157–58 collecting 30 Proust, Joseph 72 obsidian 174, 257, 278, 280 and phyllosilicate minerals proustite 49, 70, 72 octagonal cut 25 195, 198 Prussian blue 157 octahedrite 76 psilomelane 94 oil (petroleum) 12, 314, 324 and sorosilicate minerals 231 pteridosperm 333 oil shale 314 and tungstate minerals 144–46 puddingstone 306 oligoclase 167, 178, 264, 275 and zeolite minerals 187, 189 pumice 257, 276, 277, 278 oligoclase feldspar 90 dikes 26 purple copper ore 50 olivenite 160–61 Pele’s hair 281 purple zircon 233 olivine 232 Pele’s tears 281 pyrargyrite 49, 65, 70, 72 pencil gneiss 288 pyramid face 20 and igneous rocks 261, 266–69, pencil “lead” 46 pyrite 12, 62 273, 285 pendeloque cut 25 penetration, twinning 19 and other minerals 102, 137, and metamorphic rocks Pentland, Joseph 55 153, 252 297–99, 301 pentlandite 55 peridot 232 and rocks 262, 293, 301, 331 and meteorites 334–37 peridotite 266 and silicate minerals 183, and other minerals 148, 182, 191 and minerals 96, 118, 192, 210 chemical formula 12 and other rocks 261, 267, 269 221, 241 gabbro 11 permineralization 305 and sulfide minerals 50, 53–57, occurrence 9 Perovski, Count Lev Alekseevich 89 olivine gabbro 265 perovskite 89, 182, 269 61, 63 omphacite 299 Perseus 247 and sulfosalt minerals 67, 71, 73 oolitic ironstone 328 petroleum 12, 314, 324 chemical formula 12 oolitic limestone 319 pharmacosiderite 165 pyritohedral crystals 62 opal 14, 172, 203, 325 phlogopite 269, 272 pyrochlore 85, 86, 272 opaline 330 phonolite 174 “pyroclastic” rocks 257 optical spar 114 phosphates 13, 147, 148–58 pyrolusite 38, 80, 98, 103 orbicular granite 259 phosphorus 147, 151, 309, 331 pyromorphite 54, 124, 143, organic minerals 13, 246, phyllite 214, 287, 294 phyllonite 289 151, 164 247–53 phyllosilicates 166, 191–206 pyrope 242 organizing collections 32–33 Pigeon Point 207 pyrophyllite 21, 194 orpiment 15, 33, 48, 58, 59, 61 pigeonite 207 pyroxene, orthochrysotile 192 pigments 196 orthoclase 11, 17, 167, 173, pinacoid face 20 and extrusive igneous rocks 273, pink diamond 47 275, 278–79 262, 270 pink topaz 234 orthogneiss 288 pisoliths 101 and intrusive igneous rocks 261, orthopyroxene 265 pisolitic bauxite 101 262, 265–66 orthoquartzite 295, 308, 310 pistachio epidote 230 orthorhombic crystal system 23 pitchblende 83 and metamorphic rocks 296–99 oval cut 25 placer deposits 24 and meteorites 335–37 oxides 8, 9, 13, 74, 75–99 plagioclase 265, 270, 273, 275, 297 and minerals 191 oxygen 74 in gabbro 11 and sedimentary rocks 317 oxyhydroxy-halides 106 sodium 262 and subvolcanic igneous rocks oysters 248–49 plagioclase feldspar 89, 261, 264, 268–70 P 267–68 in pyroxenite 267 plaster of Paris 131, 323 pyroxene hornfels 267 palladium 38 plate tectonics 318 pyroxenite 266, 267 pallasites 334, 336 platinum 38, 265, 272 pyrrhotite 55 panning 24, 28 pleochroism 153 parachrysotile 192 pleonaste 96 Q paragneiss 288 plug, volcanic 256 pararealgar 58 plush copper ore 87 quarries 28–29 Paris, plaster of 131, 323 plutonic intrusive rocks 26, 256 quartz 9, 17, 168, 258–59 peacock ore 50 Plymouth Rock 263 pearl 243, 246, 248 polishing, gems 25 and carbonate minerals 117, 121 pearly talc 193 polyps 247 and igneous rocks 260, 262–65, peat 253 porphyritic granite 259 pebble-conglomerate 306 porphyroblasts 292, 294 268, 274, 278–80 pegmatite 259, 260 porphyry 181, 271 and metamorphic rocks 288, porphyry copper 57 and cyclosilicate minerals potash 106–07, 111 290–91, 293–95, 297, 301 223–25 potash mica 195 and native elements 37, 42–43 potassium 107, 111, 309 and other minerals 101, 141, and feldspar minerals 173, 175, potassium bentonite 200 177–78 potassium magnesium chloride 107 144, 161 powder, talcum 193 and oxide minerals 78, 90 and feldspathoid minerals 184 precipitation 305 and sedimentary rocks 306, 310, and inosilicate minerals 209 and nesosilicate minerals 312–13, 316–17 and silicate minerals 166–67, 234–36, 238, 240, 244 169, 170–71, 186, 194, 203, 223, 226, 231, 236, 241 and sulfide minerals 50, 51, 53, 57–58, 61 and sulfosalt minerals 66, 73 cementing agent 304 cryptocrystalline 331