108 



AQUEOUS BOCKS 



Fig. 8. — Pyroxene partially 

 altered to serpentine. 



Several varieties of serpentine are popularly recognized. 

 Precious or noble serpentine is simply a very pure compact va- 

 riety of a deep oil-yellow or green color. Amianthus, or chryso- 

 tiUf as noted above, is the name given to the fibrous variety. 



WilUamsite is a deep bright green, trans- 

 lucent, and somewhat scaly variety, oc- 

 curring associated with the chrome iron 

 deposits in Fulton township, Lancaster 

 County, Pennsylvania. Deweylite is a 

 hard, translucent variety occurring in 

 veins in altered dunite beds. Bowenite 

 is a pale green variety forming veins in 

 limestone at Smithiield, Rhode Island. 

 PicroUte, marmolite, and retinolite are 

 varieties of minor importance. Serpen- 

 tine alone, or associated with calcite and 

 dolomite, forms a beautiful marble, to 

 which the names verd antique, opiate, 

 and opJiiohte are given. The so-called 

 Eozoon Canadense, a supposed fossil rhizopod, is a mixture 

 of serpentine and calcite or dolomite. The name serpentine is 

 from the latin serpentinus, serpent-like, in allusion to its green 

 color and often mottled appearance. 



Those serpentines which were derived from basic eruptives, 

 or complex metamorphic rocks are described with those rocks 

 with which, in their unaltered state, they would naturally be 

 grouped. 



The mineral steatite, or talc, when pure, differs from ser- 

 pentine in containing 63.5% of silica, 31.7% of magnesia, and 

 4.8% of water. Its common form is that of white or greenish 

 inelastic scales, forming an essential constituent of the talcose 

 schists. As is the case with serpentine, it sometimes results 

 from the alteration of eruptive magnesian rocks, such as the 

 pyroxenites, and rarely occurs as a direct result of precipitation. 

 Pyrophyllite, or agalmatolite, is a hydrous silicate of alumina, 

 somewhat harder than talc, which it otherwise resembles, and 

 which is used in making slate pencils and small images. It 

 occurs in a schistose form in the Deep River region of North 

 Carolina. 



Kaolin, also a hydrous silicate of alumina, is a chemical 

 product in that it is a residue left by the chemical decomposi- 



