460 GEOLOGY. 



REFERENCE LIST OF THE MORE COMMON MINERALS. 



Actinolite — a magnesium-calcium-iron amphibole (q.v.); commonly bright 

 green to grayish green; crystals usually slender or fibrous. 



Agate — a banded or variegated chalcedony (quartz, q.v.). 



Alabaster — a fine-grained variety of gypsum (q.v.), either white or delicately 

 colored. 



Albite — a soda feldspar (q.v.), an aluminum-sodium silicate; H. 5-6; cleavage 

 perfect in two planes; luster vitreous or pearly white; occasionally bluish 

 gray, reddish, greenish; sometimes opalescent. 



Amethyst — a variety of quartz of purple or bluish-violet color, due probably 

 to manganese. 



Amphibole — the type of an important group of rock-forming minerals known 

 as the amphibole or hornblende group; a ferromagnesian silicate, monoclinic, 

 H. 5-6; luster vitreous to pearly; fibrous varieties often silky; black, ranging 

 through various shades of green to light colors ; embraces the magnesium-calcium 

 varieties, tremolite and nephrite; the magnesium-calcium-iron variety actinolite; 

 the aluminous-magnesium-iron-calcium variety hornblende, and others. 



Analcite — analcine, one of the zeolites; a hydrous aluminum-sodium silicate; 

 luster vitreous, colorless, white; occasionally grayish, greenish, yellowish, reddish, 

 transparent to opaque. 



Andesine — a plagioclase feldspar (q.v.) ; a sodium-calcium-aluminum silicate, 

 intermediate in composition between albite and anorthite; H. 5-6; white, gray, 

 grayish, yellowish, flesh red; luster sub vitreous, inclining to pearly. 



Andalusite — an aluminum silicate; luster vitreous; whitish, rose red, flesh 

 red, variety pearly gray, reddish brown, olive-green; H. 7.5, infusible; impurities 

 sometimes so arranged in the interior as to exhibit a colored, crossed, or tesselated 

 appearance in cross-section (chiastolite) . 



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 de- 

 rived 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, charac- 

 terized 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. 



