THE HALOID COMPOUNDS 



331 



FLUORITE 



Fluorite. Calcium fluoride, CaF 2 ; Ca = 51.1, F = 48.9; 



Isometric; Type, Ditesseral Central; Common forms, c (100), 

 o i 1 1 1 ), d ( 1 10), e (210), t (421) ; Twinning plane 111, interpene- 

 t rat ing ; Cleavage, octahedral perfect ; Brittle, fracture conchoidal 

 to splintery ; H. = 4 ; G. = 3.01-3.25 ; Color, white, various 

 shades of yellow, green, blue, brown, and red; Streak, white; 

 I, uster, vitreous; Transparent to nearly opaque ; n = 1.434. 



B.B. Fuses at 1387C. to an enamel, yielding a reddish flame 

 (Ca). The ignited fragment reacts alkaline with turmeric paper. 

 \Yith potassium bisulphate in the closed tube shows fluorine. 



General description. Crystals are beautifully developed and 

 very common, usually cubic in habit : simple octahedrons are less 



Fia. 408. Fluorite and Calcite from Weardale, England. 



common, but occur at Chamonix and St. Gothard, Switzerland; 

 at Spit/enberg, and in Colorado. They are usually pink or rose- 

 colored, with drusy faces, caused by repeated growths of small cubes. 



