GUIDE TO THE MINEIiALOGIC COLLECTIONS 



65 



Fluorite (fluor spar) CaP , 



Fluorite is the fluorid of calcium and contains 48.9# fluorin 

 and 51.1# calcium. 



The isometric crystals of fluorite exhibit many interesting 

 forms, some of which are shown in fig. 177-79. Penetration 



Fig. 177 Fig. 17S Fig. 179 



Fluorite 



twins are quite common (pi. 18J. The crystals are vitreous, 

 transparent and of a great variety of colors, white, yellow, 

 greenish blue, purple and green being most common; white, pink, 

 red, sky-blue and other colored varieties are often found. Mas- 

 sive varieties sometimes show irregular banding of different 

 colors. Granurar and fibrous occurrences are less frequent. All 

 varieties are characterized by perfect cleavage parallel to the 

 octahedron, which can be frequently traced in the crystallized 

 specimens, as in pi. 18 2 . 



Fluorite is found in beds, or more often in veins, in gneiss, 

 slate, limestone and sandstone; it frequently occurs as the 

 gangue of metallic minerals, notably lead ores. Fluorite occurs 

 in many parts of England and Saxony; also in Rosiclare 111. 

 where it is mined in large quantities, in Jefferson and St Law- 

 rence counties, X. Y. and in several other states. 



Fluorite is used as a flux in some metallurgic processes, also 

 in the production of opalescent glass, enameled cooking ware 

 and hydrofluoric acid. 



Cryolite Na 3 AlF 6 



Cryolite is a fluorid of sodium and aluminium, containing 54.4^ 

 fluorin, 12.8^ aluminium and 32.8^ sodium. 



The monoclinic crystals of cryolite frequently present a cubic 

 aspect due to the fact that the f3 angle is nearly 90° and the 



