SILK ATI >, TITAN \TI.S. I.T<\ 



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enstatite; large masses of serpentine, often impure, re-ult from the 

 alteration of rocks containing these minerals. Magnesium sili- 

 cates yield much 

 of their associateil 

 bases, as calcium 

 and iron, to per- 

 colating water 

 containing carbon 

 dioxide, as hicar- 

 honates, the mag- 

 nesium remaining 

 behind in the basic 

 form as serpen- 

 tine. Pseudo- 

 morphs of serpen- 

 tine after such 

 minerals as oliv- 

 ine, amphibole, 



and pyroxene re- FIG. 51 1. Serpentine with Veins of Fibrous Chrysotile. 

 suit from this Vernon, New York. 



method of altera- 

 tion. Magnesium may also be carried in solution by the percolating 

 waters as a bicarbonate, which will replace calcium or iron in sili- 

 cates, again forming serpentine; pseudomorphs formed by this 

 method after minerals which contain no magnesium, as the feld- 

 spars and even quartz, are common. 



Serpentine is itself decomposed by percolating waters, especially 

 those of solfataric origin, yielding its magnesium as a sulphate or 

 carbonate, leaving the silica free as quartz or opal. Brucite is 

 also a product of the decomposition and hydration of serpentine. 



From the many sources from which it may be derived serpentine 

 is necessarily a very widely distributed mineral. It occurs in large 

 bodies, and associated with it in many instances are deposits of 

 chromite and nickel ores, as at Bare Hill, Maryland, and Texas, 

 Lancaster County, Pennsylvania. 



Massive serpentine is quarried as a building stone, and when 

 polished is known in the trade as serpentine marble. When mixed 

 \\ith carbonates, which it often is, it forms the mottled green 

 " verdi antique." Serpentine is often disseminated through dolo- 

 mites, where it has arisen from the alteration of contained silicates 

 rather than from the magnesium of the carbonates. 



