BISILICATES. 



245 



of a white color, along with garnet ; at Boonville, in bowl- 

 ders with garnet and pyroxene ; Grenville, Lower Canada ; 

 in Bucks County, Pennsylvania ; at Keweenaw Point, Lake 

 Superior. Edelforsite is impure wollastonite. 



Pyroxene.— Augite. 



Monoclinic. / A / 

 the sides of this prism, and also distinct parallel with the 



87° 5'; cleavage perfect parallel with 



6 



2. 



m 



Hi I J 



W: 



diagonals. Usually in thick and stout prisms, of 4, 6 or 8 

 sides, terminating in two faces meeting at an edge. lAi-i 

 = 133° 33', I A {-1 = 136° 2T; 1 A 1 = 120° 32'. Massive varie- 

 ties of a coarse lamellar structure ; also fibrous, fibres often 

 very fine and often long capillary. Also granular, usually 

 in coarse granular and friable masses ; grains usually angu- 

 lar ; sometimes round ; also compact massive. 



Colors green of various shades, verging to white on one 

 side and brown and black on the other, passing through 

 Hue shades, but not yellow. Lustre vitreous, inclining to 

 resinous or pearly ; the latter especially in fibrous varieties. 

 Transparent to opaque. H. = 5-6. G.*=3-2~3'5. 



Composition. R0 3 Si; in which R may be Ca, Mg, Fe, 

 Mn, and sometimes Zn, K 2 , Na 2 , these bases replacing one 

 another without changing the crystalline form, of which 

 two or more are usually present ; the first three are most 

 common. Calcium is always present. The following is an. 

 analysis of a typical variety : Silica 55 # 0, lime 23*5, magne* 

 sia 16*5, manganese protoxide *5, iron protoxide 4 "5 = 100. 

 Fuses B.B., but its fusibility varies with the composition, 

 and the ferriferous varieties are most fusible. Insoluble in 

 acids. 



Biff. Its crystalline form, and its ready cleavage in tAvo 

 planes nearly at right angles to one another, are the best 

 characters for its determination. 



Vakieties. — The varieties may be divided into three sec- 



