GUIDE TO THE MIXERALOGIC COLLECTIONS 97 



It occurs in short ortkorhombic prisms and glassy quartzlike 

 masses of a prevailing blue color which is deeper in one direction 

 and more grayish or yellowish in a direction at right angles to 

 the first. 



It occurs in gneiss or granite but rarely in .volcanic rocks. 



Orthosilicates 

 Nephelite (nephelin) KoNa G Al s Si 9 34 



Xephelite is an orthosilicate of sodium, potassium and alu- 

 minium. 



The crystals are hexagonal-hemimorphic, prismatic in habit, 

 terminated with a basal pinacoid sometimes slightly modified 

 by a low pyramid. The crystals are small, sometimes trans- 

 parent, with a vitreous luster, and are colorless, white or faintly 

 yellow. Colorless or white glassy grains are found in some 

 eruptive rocks. A common variety, called elaeolite, occurs in 

 indistinct crystals or masses of a peculiar greasy luster and red- 

 dish brown or greenish in color. 



Xephelite occurs in the more basic igneous rocks as the 

 product of a magma rich in soda. The crystallized variety is 

 found associated with epidote and vesuvianite in lavas and other 

 eruptive rocks, notably in the lavas of Vesuvius. Elaeolite 

 occurs in granular crystalline rocks and is found in Maine, 

 Arkansas, Texas and elsewhere. 



Cancrinite 



An orthosilicate of sodium, calcium and aluminium generally 

 found in yellow to white masses associated with elaeolite and 

 blue sodalite. 



It is found in the Urals, in Norway and at Litchfield and 

 Gardiner Me. 



Sodalite Na,(AlCl)AL(Si0 4 ) 3 



Sodalite is a chlorosilicate of sodium and aluminium. It is 

 found in bright blue to gray masses of a vitreous to greasy 

 luster, in concentric nodules resembling chalcedony and rarely 

 in isometric dodecahedral crystals. 



It is formed from elaeolite and its mode of occurrence is 

 similar to thai mineral. 



