426 MINERALOGY 



Diallage is the usual pyroxene of gabbro; in the diorites and 

 norites it is associated with hornblende and hypersthene. The dark 

 colored varieties, as augite and segirite, are more often associated 

 with nepheline in the elseolite-syenites and with leucite in the 

 recent alkali lavas. Pyroxenes occur less frequently with the 

 schists and sparingly as a metamorphic product associated with 

 limestone. The green sodium pyroxene, jadeite, is never in indi- 

 vidual crystals, but occurs in very tough and compact masses, 

 breaking with a splintery fracture. It is much prized by the Chinese, 

 who have used it for ages as a material out of which they carve 

 ornaments. It is one of the minerals commonly known as jade. 

 An alteration characteristic of pyroxene is uralitization, in which 

 there is a physical change from pyroxene to a fibrous amphibole 

 with little or no chemical change ; the fibers of the uralite always 

 lie parallel to the c axis ; the formation of epidote or zoisite may 

 accompany uralitization. Those varieties containing much mag- 

 nesium are apt, in their weathering, to form talc, serpentine, and 

 bastite, while the calcium will form calcite; when more iron is 

 present, biotite, chlorite, and calcite are produced. 



Pyroxenes are easily crystallized from the fusion of their con- 

 stituents in open crucibles. They are common minerals of blast 

 furnace slags. 



SPODUMENE 



Spodumene. Lithium aluminium metasilicate, LiAl(SiOs)2 ; 

 Li 2 O = 8.4, A1 2 O 3 = 27.4, SiO 2 = 64.5 ; Monoclinic ; Type, 

 Digonal Equatorial ; & : b : c = 1.1283 : 1 : .6234 ; p = 69 32' = 

 001 A 100 ; 100 A 1 10 = 46 30' ; 001 A 101 = 33 25' ; 001 A 01 1 = 

 30 47' ; Common forms, c (001), a (100), b (010), m (110), p (110) ; 

 Twinning plane parallel to 100; Cleavage prismatic 87 perfect; 

 Brittle; Fracture, uneven; H. = 6.5-7; G. = 3.13-3.20; Color, 

 gr.ay, yellowish, green, or purple ; Streak, white ; Luster, vitreous 

 to pearly ; Transparent to opaque ; for optical properties see table, 

 page 420. 



B.B. Fuses easily to a clear glass, yielding a lithium flame 

 especially with the potassium bisulphate flux. Insoluble in acids. 



General description. Crystals are elongated in habit, parallel 

 to the vertical axis, with striations on the prism zone lengthwise. 

 At times they are of enormous size, as at the Etta mine in South 

 Dakota, where it is said that crystal faces forty feet in length have 



