80 



GEOLOGY 



Pyrite. Iron pyrites, fool's gold, iron sulphide; isometric; commonly 

 in cubes; H. 6-6.5; luster metallic, splendent, or glistening; pale brass-yellow ; 

 occurs widely disseminated throughout a large class of rocks; usually harder 

 and lighter in color than copper pyrites, and deeper in color than marcasite, 

 which has the same composition. 



Pyroxene. The type of a large and important group of rock-forming 

 f erromagnesian minerals ; varies in composition and embraces a large number 

 of varieties; usually a magnesium-iron-calcium silicate; crystals usually 

 thick and stout, but varying greatly; sometimes lamellar and fibrous; H. 

 5-6; luster vitreous inclining to resinous; green of various shades verging 

 occasionally towards light colors, more often to browns and blacks; among 

 the minerals belonging to the pyroxene group are augite, bronzite, diallage, 

 diopside, enstatite, hypersthene, and others. 



Fig. 50. 

 Fig. 50. Pyroxene crystals. 



Fig. 51. 

 Fig. 51. Quartz crystals. 



Quartz. Crystallized silica; hexagonal; crystals commonly six-sided 

 prisms capped by six-sided pyramids; without cleavage; H. 7; hard enough 

 to scratch glass; usually transparent, glassy, colorless when pure; shaded 

 by impurities to yellow, red, brown, green, blue, and black; varieties, ame- 

 thyst, purple or violet; false topaz, yellow; rose-quartz, smoky quartz, 

 milky quartz, etc. ; chalcedony is a cryptocrystalline (crystals not visible) 

 variety; carnelian, a red chalcedony; agate, a variegated or banded chal- 

 cedony; moss-agate, a chalcedony containing moss-like or dendritic crystal- 

 lizations of iron or manganese oxide; onyx, chalcedony in layers; jasper, 

 an opaque, colored quartz, usually red or brown; flint, an opa<|u<- impure 

 chalcedony; chert, an ill-defined term applied to an impure flinty rock; 

 hornstone, a translucent, brittle, flinty rock. 



Serpentine. A hydrous magnesium silicate; usually in pseudomorphic 

 forms; also fibrous, granular, cryptocrystalline, and amorphous; H. 2.5-4; 

 luster subresinous to greasy, pearly or earthy, resinous or wax -like; feel, 

 smooth and somewhat greasy; leek-green to blackish green and siskin green 

 verging into brownish and other colors; apparently derived most commonly 



