GUIDE TO THE MINERALOGIC COLLECTIONS 



113 



Serpentine and talc division 

 Serpentine H 4 Mg 3 Si.,0 9 



Serpentine is a hydrous magnesium silicate with some of the 

 magnesium replaced by iron. 



Serpentine occurs only in massive forms and in pseudo- 

 morphs after crystals of chrysolite, amphibole, pyroxene, ensta- 

 tite, etc. It is sometimes foliated but also occurs in delicate 

 silky fibers (pi. 3J and in fine granular to impalpable masses. It 

 is characterized by a greasy feel. The color is green of various 

 shades, yellow, brown, red, black and nearly white, often gray 

 on exposure and frequently variegated. The luster is greasy, 

 silky or waxy. 



Serpentine is a secondary mineral resulting from the altera- 

 tion of certain magnesium silicates and frequently forms large 

 rock masses. When formed from the alteration of basic igne- 

 ous rocks it is associated with spinel, garnet, chromite and some- 

 times ores of nickel. The variety derived from the decomposi- 

 tion of metamorphic rocks is commonly accompanied by dolo- 

 mite, magnesite and other carbonates. A variegated rock of 

 the latter type is polished for ornamental purposes and goes by 

 the name of verd antique marble; this is quarried at Milford Ct. 

 A fibrous variety known as chrysotile is mined in Quebec and is 

 used as asbestos. Outcrops of serpentine are found in West- 

 chester county at New Rochelle, Eye and Port Chester, and in 

 Putnam, Orange, Richmond, Jefferson and St Lawrence counties, 

 X. Y. 



Talc (steatite, soapstone) H 2 Mg,(SiO.,) 4 



Talc is an acid metasilicate of magnesium. 



Owing to the extreme rarity of crystallized specimens its sys- 

 tem of crystallization is still in doubt. It commonly occurs in 

 foliated or fibrous masses (pi. 3 2 ), sometimes with a stellated 

 structure, and in coarse or fine granular to compact masses. 

 These vary in hardness (Hl-1.5) but are in general very soft 

 with a soapy feel. The color is ordinarily white, oreenish or 

 gray and the luster pearly or waxy. 



VARIETIES 



Foliated talc. A light green to white foliated variety which 

 may be separated into thin, inelastic plates. 



