Anhydrite—a calcium sulphate; H. 3–3.5; luster pearly to vitreous; white, sometimes bluish or reddish; differs from gypsum in absence of water and in its greater hardness.
Anorthite—a plagioclase feldspar (q.v.); a calcium-aluminum silicate; varies much by impurities and admixtures; H. 6–6.5; pearly or vitreous luster; white, grayish, reddish.
Anthracite—hard coal; hydrocarbon with impurities; supposed to be derived from bituminous coal by metamorphism.
Antimony—a native metal, tin-white, brittle; rather rare in native form.
Apatite—essentially calcium phosphate with chlorine or fluorine; hexagonal; H. 5; luster vitreous or subresinous; colors usually greenish to bluish, characterized by a hexagonal form.
Aragonite—a calcium carbonate; differs from calcite in cleavage, and in being orthorhombic; H. 3.5–4; luster vitreous or resinous; white, also gray, yellow, green, and violet.
Asphaltum—asphalt; mineral pitch, bitumen; a natural mixture of different hydrocarbons; odor bituminous; melts at 90 to 100 degrees C.; burns with a bright flame; graduates into mineral tars and through these into petroleum; probably the residue of the latter.
Augite—one of the pyroxenes (q.v.); an aluminum-calcium-magnesium-iron silicate; H. 5–6; monoclinic, crystals usually thick and stout; sometimes lamellar; also granular; black, greenish black, deep green; an important rock-forming mineral.
Beauxite—essentially hydrated alumina; occurs in concretionary grains of clay-like form, whitish to brown; valuable as a source of aluminum.
Beryl—a beryllium-aluminum silicate; hexagonal; prismatic; H. 8; luster vitreous or resinous; marl-green, pale passing into whitish; closely resembles apatite, but distinguished by superior hardness and in composition.