424 



MINERALOGY 



twins and repeated, parallel to 001 producing striations and 

 parting ; Cleavage, prismatic at 87 12' perfect, a less so ; Brittle ; 

 Fracture, conchoidal; H. = 5-6; G. = 3.2-3.6; Color, white, 

 green to brown ; Streak, white to gray ; Luster, vitreous to dull ; 

 Transparent to opaque; a= 1.6707; p = 1.6776; Y = 1.6996; 

 y - a = .0289; Optically (+) ; Axial plane = 010; Bx a A c = 38 

 in front ; 2 V = 59 70'. 



B.B. Fusibility below five, but varies with the composition. 

 If much iron is present, it may become magnetic in R. F. on coal. 

 Generally insoluble in acids. 



General description of the pyroxenes. In habit the crystals 

 are short, stout prisms, rarely much elongated except in acmite 

 and diallage. The pinacoids are well developed and usually ter- 

 minated by the plus and minus unit pyramids. In some speci- 

 mens the two end terminations may differ, indicating a symmetry 

 lower than that of digonal equatorial. Diopside is the light-colored 

 variety and contains but little iron and aluminium, while the 

 dark opaque varieties are augite. Jeffersonite is a variety from 

 Franklin, New Jersey, containing zinc; and schefferite is a man- 

 ganese variety from Sweden. Hedenbergite is a dark green variety 

 containing iron, which replaces most of the calcium; it was first 

 described by Berzelius as from Sweden. Diallage is a variety 



elongated in habit, and 

 in most instances is lam- 



inated or even fibrous 

 g^^^ ^fe parallel to 010; it may 



M be intergrown with the 

 3% ^M^B orthorhombic pyroxenes 



and exhibit the same 

 " schiller " character] stic 

 of those varieties. 



In thin sections it is 

 either in polygonal out- 

 line, rounded, or irregu- 

 lar. When crystals are 

 well formed they are eight- 

 sided in section, formed 



by the two pinacoids and the unit prism. The color varies from 

 colorless in diopside, through various shades of green and brown, 

 in augite or acmite, the color depending upon the amount of iron 



FIG. 471. Augite Crystals. Bilin, Bohemia. 



