462 GEOLOGY, 



submetallic; iron black to brownish black; opaque; sometimes magnetic; re- 

 sembles magnetite. 



Chrysolite — olivine; essentially a magnesium-iron silicate; orthorhombic ; 

 H. 6-7; luster vitreous; green, commonly olive-green, sometimes yellow, 

 brownish, grayish green; highly infusible; a common constituent of certain 

 basic igneous rocks; the name olivine is more commonly used by geologists. 



Chrysotile — a delicately fibrous variety of serpentine (q.v.). 



Corundum — alumina; an oxide of aluminum; H. 9; rhombohedral ; large 

 crystals usually rough; luster vitreous; color blue, red, yellow, gray, and nearly 

 white; purer forms of fine colors are sapphires; the red variety is ruby, the yel- 

 low, oriental topaz, the green, emerald, and the purple, amethyst; dark colors, 

 with iron oxide, emery. 



Delessite — a ferruginous chlorite, usually olive-green or blackish green; oc- 

 curring commonly in the cavities of amygdaloids. 



Diallage — a variety of pyroxene (q.v.); H. 4; characterized by thin folise; 

 usually grayish green to grass-green, or deep green; luster on cleavage surface 

 pearly, sometimes metalloid or brassy; an essential mineral in the gabbros, as 

 sometimes defined. 



Elaeolite — a variety of nephelite (q.v.) ; occurring in large coarse crystals 

 or massive, with greasy luster, from which the name is derived; a characteristic 

 constituent of elaeolite syenite. 



Enstatite — one of the pyroxenes; essentially a magnesium silicate; ortho- 

 rhombic; H. 5.5; luster a little pearly on cleavage surface; metalloidal in the 

 bronze variety (bronzite); grayish white, yellowish white, greenish white to 

 olive-green and brown; very infusible; a common mineral in certain basic crystal- 

 line rocks. 



Epidote — -a complex aluminum-calcium-iron silicate of varying composition; 

 monoclinic; H. 6-7; luster vitreous, pearly, or resinous ; color usually pistachio- 

 green, or yellowish green to brownish green; can usually be detected by its peculiar 

 pistachio hue, which is seldom found in other minerals ; common in many crystal- 

 line rocks, usually as a secondary product. 



Feldspar — a group of minerals of the first importance in rock formation, em- 

 bracing orthoclase, microcline, albite, oligoclase, andesine, labradorite, anorthite, 

 and numerous variations; aluminum silicates, with either potassium, sodium, 

 or calcium or two or more of these ; crystallizes in both the monoclinic and tri- 

 clinic systems; possesses very distinct cleavage in two directions; H. 6-6.5; 

 range in color from white through pale yellow, red, or green, and occasionally 

 dark; triclinic feldspars frequently called plagioclase (see individual feldspars). 



Fluorite — fluorspar; calciuni fluoride; isometric, usually cubic; H. 4; luster 

 vitreous, sometimes splendent; white, yellow, green, rose, crimson red, violet, 

 sky-blue, and brown; yellow, greenish, and violet most common; occurs usually 

 in veins or cavities in beautiful crystalline form. 



Galenite — galena; lead sulphide; isometric, usually cubic; perfect cubic 

 cleavage; luster metallic; lead-gray; a common ore of lead; occurs in veins and 

 layers, also as linings of cavities. 



Garnet — a complex silicate of varying composition, embracing aluminum, 

 calcium, magnesium, chromium, iron, and manganese, but usually only two or three 



