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These 81 color photos are for the McGraw-Hill Geoscience Supersite. Chapter numbers correspond to those in MINERALOGY: A Geologist's Point of View (McGraw-Hill, 2002) XP = crossed polars PPL = plane polarized light Keck Museum/MSM = Keck Museum at the Mackay School of Mines, University of Nevada -Reno. Acanthite Ag2S Monoclinic o Hydrothermal (epithermal) environment. (chapter 12) - High grade silver-gold ore from the Comstock Lode, Virginia City, Nevada. Well-formed pyrite (white with several crystal faces), quartz far right and lower left (black) was followed by intergranular crystallization of chalcopyrite (dull yellow, far right), acanthite (gray) and gold (golden yellow, central area). The softness of acanthite and gold is indicated by a high density of scratches acquired during preparation of the polished section. Reflected light. View width is 0.5 mm. Specimen provided by the Smithsonian Institute. Amethyst SiO2 Hexagonal-trigonal o Hydrothermal environment associated with mafic volcanism. (chapter 12) - Large tubular geode from Rio Grande do Sul, Brazil. Crystals face central void and grade to clear quartz toward agate substrate (gray) of geode margin. Long dimension of geode is 24 cm but this is a section normal to the longest direction of the geode tube. Broadening of amethyst crystals due to Brazil twinning on {010} and {011} with a {110} composition surface. Amethyst SiO2 Hexagonal-trigonal o Hydrothermal environment. (chapter 12) - Hexagonal prisms with terminating faces of positive and negative rhombohedra. Largest crystal length is 5 cm. Vera Cruz, Mexico. Keck Museum/MSM. Anatase TiO2 Tetragonal o Hydrothermal environment. (chapter 12) - Dipyramid {011} with elongation in c-axis direction. Crystal width is 1.2 cm. Anglesite PbSO4 Orthorhombic o Supergene (low-T aqueous, weathering) environment. (chapter 13) - Galena (metallic gray) partially replaced by microcrystalline anglesite (dull gray to white, locally colloform) and associated "limonite". The Fe-oxyhydroxides are probably residual after pyrite. View width is 8 mm. Keck Museum/MSM Anhydrite CaSO4 Orthorhombic o Hydrothermal (alteration) environment (chapters 12 and 18). - Anhydrite crystals (up to 2nd order yellow interference colors) in twinned plagioclase (black/light gray strips). Reactive replacement involves liberation of Ca from the plagioclase that reacts with incoming sulfate-bearing aqueous solutions. Thin section view (1 mm wide) with XP. Specimen provided by the Smithsonian Institute (Comstock Mining District, sample no. 72317). Anhydrite CaSO4 Orthorhombic o Hydrothermal (precipitation) and parametamorphic environments (chapters 12, 14, and 18) - Cleaved anhydrite (pseudocubic cleavage) associated with small quartz crystals (upper left). Hand specimen width is 6 cm. Specimen supplied by H. Gordon. Anhydrite CaSO4 Orthorhombic o Hydrothermal (precipitation) and parametamorphic environments (chapters 12, 14, and 18) - Recrystallized anhydrite-calcite rock. Cleavage-controlled plucking of large central anhydrite crystal occurred during preparation of thin section, generating variable thicknesses within the anhydrite. This accounts for the variable presenting birefringence (ranging from 1st order white to 2nd order blue). Note twin lamella in the anhydrite grains. Thin section view (XP)(0.6 mm wide). Annabergite Ni3(AsO4)28H2O Monoclinic o Supergene (low-T aqueous, weathering) environment. (chapter 13) - Green annabergite occurs along fracture directions in niccoline (bronzy host, NiAs), is a fine example of how a mineral association can be very useful in mineral identification. Hand specimen view is about 6 cm. Keck Museum/MSM. Apophyllite KCa4(Si4O10)2F8H2O Tetragonal o Hydrothermal in cavities of basalt. (chapter 12). - Cluster of crystals (longest about 1.5 cm) with well-developed tetragonal prism terminated by the dipyramid {011}. Poona, India. Sample provided by H. Gordon. Aurichalcite (Zn,Cu)5(CO3)2(OH)3 Monoclinic o Supergene (low-T aqueous, weathering) zone in mineral deposit containing Cu and Zn. (chapter 13) - Tuft-like fibrous clusters (blue-green) associated with encrusting druse of hemimorphite (white) [Zn4Si2O7(OH)2.H2O] in lensoid rock cavity. Blue-green distinguishes this carbonate mineral from malachite (green) and azurite (blue). Azurite Cu3(OH)2(CO3)2 Monoclinic o Supergene (low-T aqueous, weathering) zone of mineral deposit containing Cu in a carbonate environment. (chapter 13) - Prismatic crystals (5 mm) perched on a colloform deposit of Fe-oxyhydroxides. Keck Museum/MSM Beryl Be3Al2Si6O18 Hexagonal o Granitic pegmatite environment. (chapter 11) - Aquamarine beryl (vitreous light bluish green) associated with muscovite (lower right). Hexagonal prisms with hexagonal dipyramid and basal pinacoid terminations. Longest crystal is 3.5 cm. Espirito Santo, Minas Gerais, Brazil. Specimen provided by H. Gordon. Beryl Be3Al2Si6O18 Hexagonal o Hydrothermal environment associated with silicic volcanic rocks. (chapter 12) - Morganite variety of beryl. The rose color is due to the presence of Mn2+. Crystal (1 cm in length) is dominated by the hexagonal prism and basal pinacoid. Violet Claim, Utah. Specimen provided by H. Gordon. Biotite K(Mg,Fe)3(AlSi3O10)(OH)2 Monoclinic o Pegmatite (magmatic) environment. (chapter 11) - Perfect cleavage {001} developed in a fragment (1-2 mm) of biotite viewed with a low-power optical microscope. Color brightness is governed by thickness, in this case ranging from colorless (transparent) (thin edges on left), through light to dark browns (translucent) to black (opaque) (right). Calcite CaCO3 Hexagonal-rhombohedral o Hydrothermal environment. (chapter 12) - Nailhead calcite crystals (largest is 2 cm in diameter) dominated by the hexagonal prism {100}. The larger crystal is terminated by faces of the "flat" rhombohedron {012} , whereas the small crystal (lower left) is terminated by faces of the {211} scalenohedron and basal pinacoid {001}. Sample provided by H. Gordon. Calcite CaCO3 Hexagonal-rhombohedral o Hydrothermal environment. (chapter 12) - Twinned (horizontal twin plane through center) scalenohedron (6 cm long) of famous amber-colored, late stage, calcite from Elmwood, Tennessee. Specimen provided by S. Klein. Canavalin and Lysozyme Rhombohedral and Hexagonal These synthetic organic crystals have been grown under conditions of zero gravity. Photos supplied by Alex McPherson, University of California, Irvine. o Canavalin is a seed storage protein from Jack Beans having a molecular weight of 147,000. Crystals 1, 4, 5, 7 and 9 are rhombohedral (space group R3), 6 is hexagonal (space group P63), and 2 and 10 have attributes of both space groups. (chapter 4) o Lysozyme is a defensive protein from hen eggs having a molecular weight of 14,500. It degrades bacterial cell walls. The crystals are tetragonal (space group P4). (chapter 4) Chalcanthite CuSO45H2O Triclinic o Water-free places in supergene zone of copper deposit. (chapter 13) - Nodular microcrystalline mass of colloform, water-soluble, chalcanthite (12 cm long). Note radial fibrous structure with fibers oriented normal to curved growth surfaces (broken surface, lower right). Keck Museum/MSM. Chalcedony and Quartz SiO2 Hexagonal-trigonal o Hydrothermal environment. (chapters 12 and 18) - Lower left portion is chalcedony (yellow, length fast) in part forming zig-zag extinction bands known as Runzelbänderung. Upper right portion consists of quartz crystals (blue, length slow) that have grown from the chalcedony substrate. Thin section with XP. Red-1 plate inserted from lower right. View width is 1.5 mm. Chalcedony SiO2 Hexagonal-trigonal and Opal SiO2H2O (paracrystalline) o Hydrothermal environment. (chapters 12 and 18) - (A) (PPL) Clear central portion (SE-NW) is layered chalcedony, formed at the expense of opaline silica (dark portion with colloform layering, NE and SW areas). - (B) (XP) Layering and fibrous nature of chalcedony is readily evident. Fibrous, weakly birefracting nature of opaline material (NE and SW) is evident indicating that this silica is not completely amorphous. - (C) (XP + Red-1) Fibers oriented SW-NE in central chalcedony zone are yellow with red-1 plate inserted, indicating fibers are length fast (confirming chalcedony). Note two thin layers that are blue-green indicating the silica here is either quartz, moganite, or quartzine (both length slow, normal to layering). NE and SW areas are dominantly bluish red indicating minimal birefraction and dominance of the magenta of the red-1 plate with XP. This material is may be fibrous opal-CT (lussatite). Thin section view is 3.2 mm wide. Chlorite (Mg,Fe,Al)6(Al,Si)4O10(OH)8 Triclinic and Monoclinic o Low-grade metamorphic environment. (chapters 14 and 18) - Thin section view (PPL) of metamorphosed (low-grade) basalt is about 1.5 mm wide. The green chlorite is characteristic of basalt converted to greenstone. The white lath-shaped crystals are plagioclase, the small brown crystals are titanite, and the off-white equant crystals are clinopyroxene. Franciscan subduction complex, northern California. Chlorite (Mg,Fe,Al)6(Al ,Si)4O10(OH)8 Triclinic and Monoclinic o Hydrothermal (deuteric) environment. (chapters 12 and18) - Deuteric alteration (hydrothermal) of biotite (mottled green to yellow interference colors) to chlorite (berlin blue anomalous interference color) along margins and along cleavage planes of the biotite. Thin section view of granodiorite (XP) is about 1 mm wide. Cinnabar HgS Hexagonal-rhombohedral o Low-temperature (epithermal) hydrothermal environment. (chapter 12) - Marcarsite-hosted cinnabar-quartz vein is 1-2 cm thick. Note bilateral zoned symmetry of vein filling characterized by early precipitation of microcrystalline cinnabar (red) followed inward by quartz (white). The vuggy medial region in quartz (left) indicates a low-pressure (open space) environment. Castle Peak Mine, Virginia Range, Nevada. Keck Museum/MSM. Cinnabar HgS Hexagonal-rhombohedral o Low-T hydrothermal environment. (chapter 12) - Cinnabar crystal on left (4 cm) is crudely rhombohedral. Upper right crystal is twinned on {001}. Poverty Peak, Nevada. Keck Museum/MSM Covellite CuS Hexagonal and Bornite Cu5FeS4 Orthorhombic o Supergene (low-T aqueous, weathering) environment. (chapter 13) - Fractured primary hydrothermal bornite (peach color) host contains secondary supergene covellite (blue) in cleavage- or fracture-controlled microveins. Some microveins contain chalcopyrite (yellow)(next to bornite) and idaite (Cu3FeS4), both minerals representing a second (post-bornite) stage of primary hydrothermal mineralization. Erzberg, New Guinea. Sample provided by Freeport Mining Company. Covellite CuS Hexagonal o Supergene (low-T aqueous, weathering) environment. (chapter 13) - Well-formed hexagonal plates (about 1 cm) of bornite (blue). Butte, Montana. Keck Museum/MSM Cuprite Cu2O Cubic o Supergene (low-T aqueous, weathering, oxide zone) of copper deposit. (chapter 13) - Cluster of cuprite cubes (largest 4 mm). Chino Mine, New Mexico. Sample provided by S. Klein. Dolomite CaMg(CO3)2 Hexagonal-rhombohedral o Low-T aqueous (diagenetic) environment. (chapter 13) - White (nonstained) rhombs of dolomite have formed from calcite (stained red) in micritic limestone. Thin section (PPL) view is 1.5 mm wide. Sample provided by J. Kepper. Eosphorite MnAl(PO4)(OH)2H2O Monoclinic (pseudo-orthorhombic) o Hydrothermal or low-T aqueous in granitic pegmatite environment. (chapter 11) - Crystals (1 mm) elongate parallel crystallographic c occur as radial aggregates with wedge-like terminations. Crystal growth on cleavelandite albite substrate. Black Hills, South Dakota. Sample provided by Keck Museum/MSM. Fluorite CaF2 Cubic o Hydrothermal activity associated with a metamorphic environment. (chapters 12 and 14) - Octahedral (unusual) fluorite (5 mm) from Broken Hill, NSW, Australia (NBHC Mine). NMV specimen M27168 (see Minerals of Broken Hill, 1982, H. K. Worner and R. W. Mitchell) Galena PbS Cubic o Hydrothermal environment. (chapter 12) - Intergrown cubes (3 cm) of galena (metallic gray) associated with three spheres of marcasite (brass-colored, right). Reynolds Co. Missouri. Specimen provided by H. Gordon. Galkhaite (Cs,Tl)(Hg,Cu,Zn)6(As,Sb)4S12 Cubic o Low-T hydrothermal (epithermal) environment. (chapter12) - Red cubes (1-2 mm) of galkhaite resemble cuprite. Getchell Mine, Nevada. Glauconite (K,Na)(Fe,Al,Fe,Mg)2(Si,Al)4O10(OH)2 Monoclinic o Diagenetic (low-T aqueous) environment in marine sediments. (chapter 13) - Pelloidal glauconite (green) in microcrystalline dolostone. Dolomite rhombs formed from micritic calcite during or after fracture-opening of the pelloid. Thin section view (PPL) is 1.5 mm wide. Gold Au Cubic o Hydrothermal (hot spring) environment. (chapter 12) - Small gold grains (lower right) in layered opaline silica associated with hydrothermal breccia. McLaughlin Mine, California. Slabbed hand specimen with view width 12 cm. Specimen provided by L. Larson. Gold Au Cubic o Hydrothermal (epithermal) environment. (chapter 12) - Gold mantled and alunitized-silicified dacite breccia fragments from Goldfield, Nevada (Florence Mine). Sequence of crystallization in open spaces is gold, then sulfides (black zone), and lastly quartz (white). Slabbed hand specimen is about 10 cm wide. Keck Museum/MSM. Grossularite Ca3Al2(SiO4)3 Cubic o Metamorphic (static thermal) environment. (chapter 14) - Grossularite (orange-brown) has formed along with diopside and clinozoisite (green) in siliceous-aluminous marl lenses and layers adjacent to limestone (now recrystallized) (white). U.S. dime scale (right) lies on a cordierite-biotite-quartz hornfels layer derived from mudstone. Marjum Formation, Notch Peak area, House Range, Utah. Gypsum CaSO42H2O Monoclinic o Oxide zone of sulfide deposit. (chapter 13) - Two crystals of selenite gypsum dominated by the broad side pinacoid [010} and faces of the prism {110}. Crystal in the rear is twinned, presenting fish-tail morphology (upper left). Crystals are 3 cm wide. Robinson Mining District, Nevada. Keck Museum/MSM. Gypsum CaSO42H2O Monoclinic o Low-T aqueous environment. (chapters 13 and 18) - Microscopic view (XP) of selenite gypsum cleavage fragment (2.5 mm) lying on the perfect {010} cleavage in mineral oil on a glass slide. The birefringence of gypsum in this orientation in a standard 30 micron thick thin section generates 1st order yellow interference color. First order yellow in this fragment view occurs only along the upper left edge. Colors increase through red, blue, green, to 2nd order yellow (crystal center) as thickness increases, where cleavage fragments have been broken away along other cleavage directions from the {010} cleavage. Gypsum CaSO42H2O Monoclinic o Low-T aqueous (groundwater) environment (chapter 13) - Cross-fiber "coconut" gypsum veins (2 cm thick) in Moenkopi Formation mudstone. Calcium sulfate solutions originated from evaporite beds in other parts of the formation or perhaps from the up-section Carmel Formation. Capital Reef National Park, Utah. Halite NaCl Cubic o Evaporitic surface water body environment (chapter 13) - Hopper halite crystals (up to 2 cm) forming an evaporite encrustation. Microcrystalline reddish mineral is burkeite [Na6(CO3)(SO4)2]. Searles Lake, California. Specimen provided by Gail Moulton and North American Chemical Corporation. Hematite Fe2O3 Hexagonal-rhombohedral o Complex environment, including hydrothermal (subaqueous exhalations), low-T aqueous (sedimentary in water bodies), and metamorphic (superposed) (chapters 12, 13, and 14) - Microcrystalline hematite-quartz (jasper)(red) associated with magnetite (black) in banded iron formation rock (taconite). Slabbed surface of hand specimen is about 5 cm wide. Michigan. Heterosite (Fe,Mn)PO4 Orthorhombic o Hydrothermal stage in granitic pegmatite environment. (chapter 11) - Poorly-formed heterosite crystals (purple) in association with quartz, cleavelandite, and muscovite. Palermo Mine, New Hampshire. Keck Museum/MSM. Heulandite (Ca,Na2)Al2Si7O186H2O Monoclinic o Low-T hydrothermal (vapor phase) in cavities in basalt. (chapter 12) - Characteristic coffin-shaped crystal dominated by {010} form is elongate in c-axis direction (2 cm). Bombay, India. Specimen provided by H. Gordon. Ice H2O Hexagonal o Parametamorphic environment (chapters 14 and 18) - Thin sections (XP) of Antarctic ice from the Taylor Dome ice core recovered in 1993. Firn-ice transition in this core is at 72 m. Thick sections cut normal to vertical core. Maximum presenting interference color blue-green is generated by crystals in which crystallographic c lies flat in the section. Since the birefringence (maximum) of ice is very low (dark gray) at standard 30 micron thickness, the sections were prepared considerably thicker in order to generate interference colors (including shades of gray) useful as indicators of crystal orientation. Fabrics in both samples are fairly well polygonalized. Note trapped air bubbles in both samples. Photos provided by J. Fitzpatrick and S. Jacobson (National Ice Core Laboratory/U.S.G.S.). (A) Coarser-grained (crystals mostly 3 cm) sample, retrieved from a depth of 411.5 m, indicates on-going recrystallization accompanied by grain rotation by means of slip on (001). This yielded near vertical orientation of crystallographic c, as indicated by the very low birefringence in most grains. (B) Finer-grained (crystals mostly 1.5 cm) sample, retrieved from a depth of 180.1 m, has little or no preferred crystal orientation, reflecting the lower deviatoric stress environment. Lazulite (Mg,Fe)Al2(PO4)2(OH)2 Monoclinic o Hydrothermal stage in granitic pegmatite environment. (chapter 11) - Crystal left of center is elongate in crystallographic c direction, whereas crystal just se of center is view down crystallographic c. Both crystals are pseudo-tetragonal, with the {111} and { 11} prisms mimicking the tetragonal dipyramid. Note spotty bluish and brownish coloration, the latter due to surface oxidation that has generated Fe-oxyhydroxides. Magnetite Fe3O4 Cubic o Biogenic (bacteria) low-T aqueous environment (chapters 13 and 16) - Magnetite (spheres) in magnetotactic bacterium shown by tapping mode atomic force microscopy. Malachite Cu3(OH)2(CO3)2 Monoclinic o Supergene (low-T aqueous, weathering, oxide zone)zone of Cu deposit. (chapter 13) - End view of stalactitic precipitate, consisting of colloform core of malachite mantled by azurite [Cu3(OH)2(CO3)2]. Formation of azurite was favored by conditions of increased partial pressure of CO2 and/or lower humidity. Diameter about 3 cm. Sample provided by H. Gordon. Mercury Hg Hexagonal-rhombohedral (below -46° C). o Low-T hydrothermal (hot spring) environment. (chapter 12) - Beads of native mercury associated with cinnabar (red) and chalcedony (white). Moganite SiO2 Hexagonal-trigonal o Hydrothermal environment. (chapters 12 and 18) - Microcrystalline, radial-fibrous SiO2 (lepispheres) moganite (or quartzine). Fibers oriented NE-SW are blue-green (XP + red-1) indicating fibers are length slow (unlike chalcedony). Thin section view is 1.5 mm wide. Neptunite KNa2Li(Fe,Mn,Mg)2Ti2Si8O24 Monoclinic o Hydrothermal environment. (chapter 12) - Elongate prism {110} of neptunite (right, 2 cm) is terminated by the {111} prism (?) and {101} pinacoid (?). Associated with benitoite (blue crystals, left) in veins cutting blueschist. San Benito Co., California. Keck Museum/MSM. Opal SiO2nH2O Poorly crystalline (paracrystalline) to amorphous. o Low-T aqueous environment (chapter 13) - Opalized wood from Virgin Valley, Nevada. The layered opalized wood structure (brown) contains "easter eggs" (3-5 mm) of fire opal that are open-space fillings of pipe-like vessels (seen in cross section) known as xylem that serve as avenues of water transport from roots to leaves. Keck Museum/MSM Orpiment As2S3 Monoclinic o Low-T hydrothermal environment. (chapter 12) - Curved prismatic crystals ( about 1 cm) elongate in c-axis direction. Gold Bar District, Nevada. Specimen provided by S. Klein. Osmiridium (Ir,Os) Cubic and Cinnabar (HgS) Hexagonal-rhombohedral o Placer environment (chapter 13) - Placer osmiridium (brown, due to oxidation of impurities) and cinnabar (red) from the American River, Sierra Nevada, California. Platy habit {001} of osmiridium is also characterized by crude pseudohexagonal outline (left). View width is 2.6 mm. Sample provided by J. Sjoberg and U.S. Bureau of Mines. Piedmontite Ca2(Al,Mn,Fe)3(SiO4)(Si2O7)O(OH) Monoclinic o Metasomatic metamorphic (chapters 14 and 18) - Piedmontite-quartz vein in metavolcanic rock of Peavine Mountain, Nevada. Prisms elongate in b crystallographic direction. One direction of cleavage parallels crystal elongation. Fractures normal to elongation represent a poor {010} cleavage. Crystals in hand specimen (not shown) are purplish red brown. Thin section view (XP) is 10.5 mm wide. Pyrrhotite Fe7S8 Monoclinic (pseudohexagonal) o High-T hydrothermal (chapter 12) - Pseudohexagonal plates {001} associated with scalenohedral calcite (white). Larger plate is 2 cm. Santa Rosalia, Mexico. Keck Museum/MSM Quartz SiO2 Hexagonal-Trigonal o Hydrothermal in granitic pegmatite environment. (chapters 11 and 12) - Two-stage growth indicated by scepter relationship, consisting of an elongate hexagonal prism (1st stage) capped with growth of doubly-terminated prismatic crystals (2nd stage). Specimen provided by S. Klein. Rhodochrosite MnCO3 Hexagonal-rhombohedral o Hydrothermal environment (chapter 12) - Growth rhombohedrons (left of center, largest 1 cm) and perfect cleavage (upper center) are characteristic. Crystals lie on a Mn-oxyhydroxide substrate. Uchucchacua Mine, Lima, Peru. Specimen provided by H. Gordon Rhodonite MnSiO3 Triclinic o Hydrothermal environment. (chapter 12). - Elongate rhodonite (pink) crystal (6 cm long) with pinacoid faces defining [001] zone. Calcite(white) association. Franklin, New Jersey. Keck Museum/MSM Rhodonite MnSiO3 Triclinic o Hydrothermal followed by weathering environment. (chapters 12 and 13) - Crystalline aggregate (12 cm wide) of rhodonite (pink) with low-T aqueous (weathering) reaction along fractures producing pyrolusite MnO2. A diagnostic association. Keck Museum/MSM Sillimanite Al2SiO5 Orthorhombic o Metamorphic in aluminous sedimentary rock (chapters 14 and 18). - Elongate sections of prisms have higher (orange-red) presenting birefringence (center crystal, 3 mm) than diamond-shaped to nearly square prism cross sections (white and grays). The cross sections characteristically have one direction of cleavage (larger crystals right of center and sw of center) unlike the similar mineral andalusite that has two directions of nearly right-angle cleavage. Thin section view (XP). Silver Ag Cubic o Supergene (low-T aqueous) environment (chapters 13 and 16) - A "silver arch" of wire native silver and other contorted wire shapes. SEI image. Keck Museum/MSM. Spurrite Ca5(SiO4)2(CO3) Monoclinic o Metasomatic metamorphic environment (chapters 14 and 18) - Sequence crystallization indicated by spurrite (youngest) mantling monticellite (light gray, CaMgSiO4), mantling merwinite (oldest, brownish, twinned, Ca3Mg(SiO4)2) core. Spurrite interference colors range up to 2nd order blue. Host is coarse-granular dolomite (very high, pastel, interference colors). Thin section view (XP) is 1 mm wide. Crestmore, California. Sulfur S Orthorhombic o Fumarolic environment (chapter 12) - Sulfur crystals on extremely altered andesite from Devil's Kitchen near summit of Mt Hood (Oregon). Larger crystals are about 1 cm. Specimen provided by R. Watters. Sulfur S Orthorhombic o Fumarolic environment (chapter 12) - Larger crystal (1.5 cm) is oriented with c-crystallographic axis vertical. The faces of the orthorhombic dipyramid {111} are not equally developed. There is an edge-beveling face of the {113} dipyramid (upper right) and there is a basal pinacoid {001}. Cianciana, Sicily, Italy. Specimen provided by S. Pullman. Talc Mg3Si4O10(OH)2 Triclinic o Metamorphic environment (chapters 14 and 18) - Talc crystal (center) in serpentine (greenish gray) and magnesite (brownish, lower area). Central area of talc crystal presents 3rd order green interference color as traced from "lower" colors appearing on tapering crystal edges. Thin section view (XP) width is 0.8 mm. Talc in hand specimen (not shown) is white and serpentine is greenish. Tenorite CuO Monoclinic o Supergene (low-T aqueous, weathering, oxide zone) zone of Cu deposit. (chapter 13) - Layered colloform submicrocrystalline tenorite (dark gray to black) associated with azurite (blue). Kimberly, Nevada. Keck Museum/MSM. Topaz Al2SiO4(F,OH)2 Orthorhombic o Hydrothermal environment associated with silicic volcanic rocks. (chapter 12) - Sherry-colored topaz (1.5 cm wide) associated with black cube of bixbyite (right of center) and quartz crystals (white). Vertical prisms are terminated by faces of other prisms, the dipyramid, and basal pinacoid. Maynard Claim, Thomas Range, Utah. Specimen provided by H. Gordon. Tourmaline NaFe3Al6B3Si6O27(OH)4 Hexagonal-trigonal o Hydrothermal in granitic pegmatite environment. (chapter 11) - Top view of a rubellite tourmaline crystal with prism-terminating forms consisting of three faces (relatively larger) of the trigonal pyramid {021}, and three edge-beveling faces of the trigonal pyramid {101}. Torbernite Cu(UO2)2(PO4)210H2O Tetragonal o Low-T aqueous in granitic pegmatite environment (chapter 11) - Square outline of crystal (lower left, 5 mm) reflects tetragonal morphology of torbernite (green). Crystals grew on cleavage-controlled fracture surface of pegmatitic K-feldspar (white) intergrown with graphic smoky quartz (dark gray). Spruce Pine District, North Carolina. V. Gianella, Keck Museum/MSM. Uraninite UO2 Cubic o Hydrothermal in granitic pegmatite environment followed by a weathering environment (chapters 11, 12, 13). - Uraninite (black) is associated with gummite (yellowish orange). Gummite consists of an assortment of oxides of U, Th, and Pb. Grafton, New Hampshire. (A) Hand specimen view width is 1 cm. (B) Thin section view (PPL) is 3 mm wide. The replacement of uraninite "lobes" by gummite is particularly evident (lower left). Vermiculite (mg,Fe,Al)3(Si,Al)4O10(OH)24H2O Monoclinic o Most commonly as a weathering (low-T aqueous) product of biotite (chapter 13). - Crystal (8 cm diameter) was expanded by heating. Sample supplied by U.S. Bureau of Mines. Vivianite Fe3(PO4)28H2O Monoclinic o Low-T aqueous environment (chapter 13) - Blades of vivianite (blue), elongate in c-axis direction, have grown on rock fracture substrate. Larger crystal (lower left, 3 cm long) has broken along perfect {010} cleavage (flat-lying) on which the near-right angle poor cleavages {100} and { o1} are apparent. Wollastonite CaSiO3 Triclinic o Metamorphic environment in siliceous carbonate rocks (chapters 14 and 18). - Thin section view (XP) width is 1.3 mm. Longitudinally sectioned twinned wollastonite crystal (right) has one twin lamella with a white interference color and the other in nearly an extinction position. Transverse section of multiply-twinned crystal (left) has two directions of nearly right-angle cleavage. Similar to tremolite except for lack of typical amphibole cleavage intersection angles. Wulfenite PbMoO4 Tetragonal o Supergene (low-T aqueous, weathering) environment of Pb-bearing deposit. (chapter 13). - Reticulated cluster of wulfenite plates. Dominant forms are basal pinacoid {001} and edge-beveling faces of the tetragonal dipyramid {101}. Plates are about 2 cm on an edge. Specimen provided by H. Gordon. Wulfenite PbMoO4 Tetragonal o Supergene (low-T aqueous, weathering) environment of Pb-bearing deposit. (chapter 13) - Reticulated wafer-thin plates of wulfenite. Lucia District, Elko County, Nevada. Donated to Keck Museum/MSM by L. Gundlach. Larger crystal with Halloween happy face is 3 cm. Zircon ZrSiO4 Tetragonal o Metamorphic environment. (chapter 14) - Well-formed zircon crystal (1.5 cm) in schist from Alta, Norway. Stout tetragonal prism is terminated by tetragonal dipyramids {011} and {021}. Specimen provided by H. Gordon. 
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