92 



NEW YORK STATE MUSEUM 



thene is found in norites and other granular eruptive rocks, a 

 series of which may be found in the vicinity of Peekskill, West- 

 chester co. N. Y. 



Pyroxene (augite) 



Pyroxene is essentially a normal metasilicate of calcium and 

 magnesium, also containing iron, manganese or zinc and some- 

 times small percentages of potassium and sodium. The many 

 varieties are usually classified as nonaluminous and aluminous. 



Fig. 20S Fig. 209 Fig. 210 



Pyroxene 



Pyroxene occurs in monoclinic crystals of prismatic habit with 

 well developed terminations (fig. 208, 209); these crystals have a 

 nearly square or octagonal cross section composed of the faces 

 of the unit prism which has an angle of 93° (nearly 90°) and the 

 faces of the ortho and clino pinacoid (fig. 210). A strongly 

 marked parting parallel to the basal pinacoid is very character- 

 istic, and is well shown in the specimen reproduced in pl.29^ The 

 crystals are often thick and short. Massive forms are granular, 

 foliated or columnar in structure but rarely fibrous. The luster 

 is vitreous, resinous to dull and the color usually some shade of 

 green, but also white, brown, or black. 



VARIETIES 



Diopsid or malacolite CaMg(Si0 3 ) 2 . Usually white or pale 

 green in color. 



Hedenbergite (CaFe) (Si0 3 ) 2 . Color grayish green to black. 



Augite. An aluminous pyroxene chiefly CaMg(Si0 3 ) 2 but con- 

 taining aluminium and iron. Color dark green, brownish green 

 to black. 



