500 MINERALOGY 



The variety chrysotile commercially known as asbestos is fibrous 

 and occurs in cross-fibred veins in massive serpentine. When the 

 fibers are soft, silky, and easily separable, they are spun and woven 

 into fireproof cloth. The poorer qualities are used for fireproofing 

 and as non-conductor coverings for steam boilers and pipes. 



Chrysotile is mined at Black Lake, .Thetford, Quebec ; in the 

 United States at Casper, Wyoming, and in northern Vermont near 

 the Canada locality. Closely related to serpentine is the silicate 

 of nickel, genthite, H 4 Mg 2 Ni 2 (Si0 4 )3 . 4 H 2 O ; as bright green or 

 yellowish green, amorphous crusts, or stalactitic, associated with 

 chromite and serpentine, at Texas, Pennsylvania, and Webster, 

 North Carolina. It is a secondary mineral derived from the ser- 

 pentine. Usually contains about 30 per cent, of NiO. 



Garnierite, also a green amorphous silicate of nickel and magne- 

 sium, H 2 (.Ni.Mg)Si0 4 , is associated with serpentine at Webster, 

 North Carolina, and at Riddle, Oregon. In New Caledonia it 

 occurs in quantities sufficient to be worked as an ore of nickel. 



Talc. A basic metasilicate of magnesium, H 2 Mg 3 (Si0 3 )4 ; 

 MgO = 31.7, SiO 2 = 63.5, H 2 O = 4.8; Orthorhombic or mono- 

 clinic, well-developed crystals are not known; Cleavage, basal; 

 H. = 1-1.5; G. = 2.7-2.8; Color, gray, or shades of green and 

 yellow ; Streak, white ; Luster, pearly to greasy ; Subtranslucent 

 to opaque; a = 1.539; p = 1.589; -y = 1.589; -y - a = .050; 

 Optically (-); Axial plane = 100; Bx a -L001; 2E = 6-40. 



B.B. Whitens, exfoliates somewhat, and fuses with difficulty 

 on the very thin edges. Ignited in the forceps with cobalt solu- 

 tions becomes flesh-colored (Mg). Insoluble in acids. 



General description. Usually massive, granular, or foliated, 

 rarely does it occur in six-sided scales. The massive variety is 

 known as soapstone or steatite. Rensselaerite is a fibrous variety, 

 pseudomorphous after enstatite or amphibole, preserving the 

 structure of the parent mineral. 



Chemically, small amounts of iron or nickel may replace the 

 magnesium. Talc is the end product, produced in the weathering 

 of a large number of silicates containing magnesium, especially 

 amphiboles and pyroxenes and often spineL It is very stable 

 under conditions of weathering, but when fused it loses water and 

 on cooling forms enstatite and quartz. 



