THE HALOID COMPOUNDS 



ite has also been produced by the condensation of vapors or by the 

 interaction of volatile fluorides with other minerals, as in the lavas 

 of Vesuvius. 



Crystalline specimens of great beauty are obtained in Cornwall 

 and ( 'uml id-land, England; at St. Gothard, Switzerland; at Amity 

 and lire \vster, and in St. Lawrence County, New York; and at 

 Castle Dome, Arizona. Fluorite is mined in large quantities along 

 the Ohio River in Illinois and Kentucky, where there are large 

 deposits, filling veins in limestone, associated with galena, sphal- 

 erite, chalcopyrite, and pyrite. They were probably formed by 

 precipitation or replacement of the calcium carbonate. Both in 

 Virginia and Colorado fluorite is produced commercially, but as a 

 by-product resulting from the mining of lead, zinc, or silver ores. 



In the United States 60,000 tons are used annually, mostly as a 

 flux in the metallurgical industries. By its use a very fluid slag, 

 melting at a low temperature, is formed, at the same time lowering 

 the sulphur and phosphorus content of the resulting iron or steel. 

 It is used in minor quantities in the production of hydrofluoric 

 acid, in enameling works, in glazes and opalescent glass. The 

 famous Blue John mine of Derbyshire, England, produces a banded 

 purple spar used for vases and other ornaments. 



CRYOLITE 



Cryolite. Sodium aluminium fluoride ; Na 3 AlF 6 ; Na = 

 32.8, Al = 12.8, F = 54.4 ; Monoclinic ; Type, Digonal Equatorial ; 

 a : fc : 6 = .9663 : 1 : 1.3882 ; p = 89 49' = 001 A 100 ; 100 A 

 110 =.44 1'; 001 A 101=55 2'; 001 A 011=54 14'; Com- 

 mon forms, a (100), c (001), m(110), d(101), r(011); Twining 

 plane 010 ; Cleavage, c quite perfect, m less so ; Brittle, fracture 

 uneven; H. = 2.5; G. = 2.95-3; Color, white, reddish, brown 

 to nearly black; Streak, white; Luster, vitreous to greasy, 

 Transparent to opaque; n = 1.36; Optically (+). Axial plane 

 perpendicular to 010; Bx. A normal to 001 = 44 5'; 2E = 59 

 24'. 



B.B. Fuses easily to a white enamel, which becomes blue with 

 cobalt solution (Al), yields a yellow flame, and the ignited frag- 

 ment reacts alkaline with turmeric paper. Fused with potassium 

 bisulphate in the closed tube shows fluorine. 



General description. Crystals are rare and exist only in the 

 cracks of the massive mineral ; as its name indicates, the massive 



