SILICATES, TTTANATES, BT 



417 



B.B. Infusible (about 1400), shows potassium with the flux 

 and blue jilass. I )ecompo>ed with H( '1 without gelatinization 

 but with the M'paratioii of silica. The solution freed of silica 

 yields a precipitate of aluminium hydroxide with ammonia. The 

 powdered mineral often becomes blue when treated with cobalt 

 solution. 



General description. Crystals are usually simple tetragonal 

 trisoctahedrons, rarely in combinations with the cube or rhom- 

 bic dodecahedrons; also in 

 rounded Drains, as in the 

 lavas of Vesuvius; seldom 

 ina<-ive. Leucite is dimor- 

 phous ; the apparently sim- 

 ple isometric crystals at 

 ordinary temperatures are 

 complex aggregates of 

 twinned lamellae, and prob- 



FIG. 466. Leucite. Vesuvius, Italy. 



ably orthorhombic. When 



heated above 500 these 



complex individuals become simple isometric crystals, losing their 



double refraction, and are isotropic. The isometric form, being 



I-'ii;. ItiT. Section of a Leucitite, showinn Rnunilrd Leucite Crystals 

 with Dark Inclusions arranged Symmetrically. 



2B 



