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Documents for "Mineralogy and Crystallography":
  • agate translucent, cryptocrystalline variety of quartz and a subvariety of chalcedony. Agates are identical in chemical structure to jasper, flint, chert, petrified wood, and tiger's-eye, and are often found in association with opal. The colorful, banded rocks are used as a...
  • alabaster fine-grained, massive, translucent variety of gypsum , a hydrous calcium sulfate. It is pure white or streaked with reddish brown. Alabaster, like all other forms of gypsum, forms by the evaporation of bedded deposits that are precipitated mainly from...
  • amber fossilized tree resin. Amber can vary in color from yellow to red to green and blue. The best commercial amber is transparent, but some varieties are cloudy. To be called amber, the resin must be several million years...
  • amethyst [Gr.,=non-drunkenness], variety of quartz , violet to purple in color, used as a gem. It is the most highly valued of the semiprecious quartzes. It is associated with a number of superstitions, being regarded as a love charm, as a potent...
  • amphibole any of a group of widely distributed rock-forming minerals, magnesium-iron silicates, often with traces of calcium, aluminum, sodium, titanium, and other elements. The amphibole minerals are...
  • anglesite pale green, blue, yellow-to-white, or colorless mineral, a sulfate of lead, PbSO 4 , that is formed by oxidation of galena , crystallizing in the orthorhombic system and occurring also in granular or massive form. It is widely distributed and commonly associated with galena and other lead minerals. It is a secondary...
  • apatite mineral, a phosphate of calcium containing chlorine or fluorine, or both, that is transparent to opaque in shades of green, brown, yellow, white, red, and purple. Apatite is a minor constituent in...
  • aquamarine [Lat.,=seawater], transparent beryl with a blue or bluish-green color. Sources of the gems include Brazil, Siberia, the Union of Myanmar, Madagascar, and parts of the United States. Oriental aquamarine is a transparent crystalline...
  • arsenopyrite or mispickel , silver-white to steel-gray mineral with the metallic luster characteristic of a pyrite. It is a sulfarsenide of iron, FeAsS, crystallizing in the orthorhombic system and occurring also in massive form. It is widely distributed and is an important source of arsenic. Often it is found...
  • asbestos common name for any of a variety of silicate minerals within the amphibole and serpentine groups that are fibrous in structure and more or less resistant to acid and fire. Chrysotile asbestos, a...
  • azurite blue mineral, the basic carbonate of copper, occurring in monoclinic crystals or masses that range from transparent to translucent and opaque. It is usually associated with malachite , which it resembles except in color; when the two minerals are very closely associated, the stone is called azurmalachite. Beautiful crystals of azurite are found in the United States in Arizona...
  • barite barytes [New Lat., from barium], or heavy spar, a white, yellow, blue, red, or colorless mineral. It is a sulfate of barium, BaSO 4 , found in nature as tabular crystals or in granular or massive form and has a high specific gravity. The mineral is widely distributed throughout the world. It often occurs in veins with lead and...
  • beryl mineral, a silicate of beryllium and aluminum, Be 3 Al 2 Si 6 O 18 , extremely hard, occurring in hexagonal crystals that may be of enormous size and are usually white, yellow, green, blue, or colorless. Beryl is commonly used as a gemstone. The refractive index is...
  • biotite iron-rich variety of phlogopite, most abdunant of the mica minerals.
  • bloodstone or heliotrope, green chalcedony spotted with red, used as a gem stone. It is found in India, the United States, Brazil, and Australia.
  • calcite very widely distributed mineral, commonly white or colorless, but appearing in a great variety of colors owing to impurities. Chemically it is calcium carbonate, CaCO 3 , but it frequently contains manganese, iron, or magnesium in place of the calcium. It crystallizes in the hexagonal system, its crystals being characterized by highly perfect cleavage. Calcite also...
  • carnelian or cornelian , variety of red chalcedony , used as a gem. It is distinguished from sard by the shade of red, carnelian being bright red and sard brownish. The red coloring is apparently caused by...
  • cassiterite heavy, brown-to-black mineral, tin oxide, SnO 2 , crystallizing in the tetragonal system. It is found as short prismatic crystals and as irregular masses, usually in veins and replacement deposits associated with granites. Since it is hard,...
  • cat's-eye gemstone that displays a thin band of reflected light on its surface when cut as a cabochon. Its name is derived from its supposed resemblance to the eye of a cat. The optical effect, known as...
  • celestite or celestine , mineral appearing in blue-tinged or white orthorhombic crystals or in fibrous masses. The natural sulfate of strontium, SrSO 4 , it is important as a source of strontium and of certain of its compounds, e.g., strontium hydroxide, used in refining beet sugar, and strontium nitrate, used in red signal flares. It occurs in...
  • cerussite colorless to white or gray mineral, sometimes yellowish or greenish, transparent to opaque, very brittle, crystallizing in the orthorhombic system and occurring also in granular and massive form...
  • chalcedony [from Chalcedon ], form of quartz the crystals of which are so minute that its crystalline structure cannot be seen except with the aid of a microscope. Chalcedony has a waxy luster and is translucent to...
  • chalcopyrite or copper pyrites , brass-yellow mineral, sometimes with an iridescent tarnish. It is a sulfide of copper and iron, CuFeS 2 . It crystallizes in the tetragonal system but is usually found in the massive form. Chalcopyrite is of primary origin and occurs in igneous and metamorphic rocks and in metalliferous veins. It is...
  • chromite dark brown to black mineral. It is an iron-chromium oxide, FeCr 2 O 4 , with traces of magnesium and aluminum. Its crystals are octahedral, but rare; it usually occurs as irregular, granular masses in association with igneous rocks, including ophiolites, which are...
  • chrysoberyl [Gr.,=golden beryl], a beryllium aluminate used as a gem. It has a vitreous luster and is transparent to translucent. The more valuable cat's-eye is a variety of chrysoberyl. Another variety, alexandrite, was first discovered in the Ural Mts. of Russia, on the birthday of Czar Alexander II, for whom it was named. It is remarkable in that it...
  • cinnabar mineral, the sulfide of mercury, HgS. Deep red in color, it is used as a pigment (see vermilion ), but principally it is a source of the metal mercury. It is mined in Spain, Italy, and in the United States in California. The mercury is obtained from it by roasting, the sulfur combining with...
  • cleavage tendency of many minerals to split along definite smooth planar surfaces determined by their crystal structure. The directions of these surfaces are related to weaknesses in the atomic structure of...
  • coal fuel substance of plant origin, largely or almost entirely composed of carbon with varying amounts of mineral matter.
  • cobaltite opaque, silver-white, sometimes reddish or grayish mineral of the pyrite group, a compound of cobalt, arsenic, and sulfur, CoAsS. It occurs in crystals of the cubic system, also in compact to...
  • corundum mineral, aluminum oxide, Al 2 O 3. The clear varieties are used as gems and the opaque as abrasive materials. Corundum occurs in crystals of the hexagonal system and in masses. It is transparent to opaque and has a vitreous to...
  • cryolite or kryolite [Gr.,=frost stone], mineral usually pure white or colorless but sometimes tinted in shades of pink, brown, or even black and having a luster like that of wax. Chemically, it is a double fluoride of...
  • crystal a solid body bounded by natural plane faces that are the external expression of a regular internal arrangement of constituent atoms, molecules, or ions. The formation of a crystal by a substance...
  • diamond mineral, one of two crystalline forms of the element carbon (see allotropy ), the hardest natural substance known, used as a gem and in industry.
  • dolomite . 1 Mineral, calcium magnesium carbonate, CaMg (CO 3 ) 2. It is commonly crystalline and is white, gray, brown, or reddish in color with a vitreous to pearly luster. The magnesium is sometimes replaced in part by iron or manganese. 2 Carbonate rock composed chiefly of the mineral dolomite, similar to limestone but somewhat harder and heavier. The rock may be metamorphosed into dolomitic marble. Most dolomites probably...
  • emerald the green variety of beryl , of which aquamarine is the blue variety. Chemically, it is a beryllium-aluminum silicate whose color is due to small quantities of chromium compounds. The emerald was highly esteemed in antiquity;...
  • feldspar or felspar , an abundant group of rock-forming minerals which constitute 60% of the earth's crust. Chemically the feldspars are silicates of aluminum, containing sodium, potassium, iron, calcium, or barium or...
  • fluorite or fluorspar , mineral appearing in various colors, e.g., green, yellow-brown, rose, and red. Chemically, it is calcium fluoride, CaF 2. Its crystals, commonly cubic, are transparent or translucent and under certain conditions exhibit fluorescence. The mineral also occurs in granular and massive forms. Fluorite is found in various...
  • galena or lead glance, lustrous, blue-gray mineral crystallizing usually in cubes, sometimes in octahedrons. It is the most important ore and the principal source of lead. It consists of lead sulfide, PbS, but frequently...
  • garnet name applied to a group of isomorphic minerals crystallizing in the cubic system. They are used chiefly as gems and as abrasives (as in garnet paper). The garnets are double silicates; one of the...
  • garnierite pale apple-green mineral, chemically a hydrous silicate of nickel and magnesium. An important ore of nickel, it is found in New Caledonia, Russia, and S Africa. In the United States it occurs in...
  • gem commonly, a mineral or organic substance, cut and polished and used as an ornament. Gems also are used as seals (items of assurance) and as talismans (good-luck charms). For birthstones, see month. ...
  • graphite an allotropic form of carbon , known also as plumbago and black lead. It is dark gray or black, crystalline (often in the form of slippery scales), greasy, and soft, with a metallic luster. It is a good conductor of electricity...
  • gypsum mineral composed of calcium sulfate (calcium, sulfur, and oxygen) with two molecules of water, CaSO 4 ·2H 2 O. It is the most common sulfate mineral, occurring in many places in a variety of forms. A transparent crystalline variety is selenite. A massive gypsum of delicate color and texture, readily...
  • hardness property of matter commonly described as the resistance of a substance to being scratched by another substance. The degree of hardness is relative, different substances being compared with one...
  • hematite mineral, an oxide of iron, Fe 2 O 3 , containing about 70% metal, occurring in nature in red to reddish-brown earthy masses and in steel-gray to black crystalline forms. Hematite that has a metallic luster is called specular hematite,...
  • Iceland spar colorless variety of crystallized calcite , characterized by its properties of transparency and double refraction. It is used chiefly in the manufacture of Nicol prisms , which are essential parts of polarizing microscopes and other optical instruments. The principal deposit is in Iceland, but small quantities are found in other countries, including the United...
  • ilmenite black mineral, iron titanium oxide, FeTiO 3 , crystallizing in the hexagonal system. It is sometimes found as tabular hexagonal crystals but occurs more commonly as small grains in igneous and metamorphic rocks and in sands derived from them...
  • jade common name for either of two minerals used as gems. The rarer variety of jade is jadeite, a sodium aluminum silicate, NaAl(SiO 3 ) 2 , usually white or green in color; the green variety is the more valuable. The commoner and less costly variety of jade is nephrite, a calcium magnesium iron silicate of varying composition, white...
  • jasper opaque, impure cryptocrystalline quartz , usually red, but also yellow, green, and grayish blue. It is used as a gem. Ribbon jasper has the colors in stripes.
  • kaolinite clay mineral crystallizing in the monoclinic system and forming the chief constituent of china clay and kaolin. It is a hydrous aluminum silicate commonly formed by the weathering and decomposition of rocks containing aluminum silicate compounds; feldspar is a chief source. Kaolinite has the same...