498 MINERALOGY 



Corundophilite, H 20 (Mg . Fe)nAl 8 Si 6 045, is associated with corun- 

 dum at Chester, Massachusetts, and Asheville, North Carolina. 

 Thuringite is a massive scaly variety occurring at French Creek, 

 Pennsylvania ; Hot Springs, Arkansas ; and at Harper's Ferry 

 inclosing garnets. 



Stilpnomelane is an iron variety having the metallic luster of 

 brass or mosaic gold, occurring at the Sterling iron mine, New York. 



Some fifteen other species and varieties could be added, most of 

 which are rare or uncertain. 



Chlorites occur as schist-forming minerals, and lining cavities or 

 filling veins in all kinds of igneous rocks, as alteration products. 

 Most schist-forming chlorites are fine and scaly, having a talclike 

 or soapy feeling ; but chemically they are easily distinguished, as 

 chlorite contains much aluminium. 



SERPENTINE 



Serpentine. H 4 Mg 3 Si 2 O 9 , or H 3 Mg 2 (Mg . OH)(Si0 4 ) 2 ; MgO 

 = 43.52, SiO 2 = 43.16, H 2 O, = 13.32; Monoclinic, never in 

 crystals ; Cleavage, basal sometimes distinct ; H. = 2.5-5.5 ; 

 G. = 2.50-2.65 ; Color, shades of green and yellow ; Fracture, 

 conchoidal or splintery ; Streak, white ; Luster, dull to resinous, 

 or greasy; feels smooth or greasy; Translucent to opaque; 

 a = 1.560 ; p = 1.570 ; y = 1.571 ; y a = .011-013 ; Opti- 

 cally ( ); Chrysotile (+); Axial plane (?) ; Bx a = c, In 

 chrysotile, _L c ; 2 V = 16-98. 



B.B. Fuses with difficulty on very thin edges. In the closed 

 tube yields water. After ignition with cobalt solution usually 

 flesh-colored (Mg) ; decomposes with HC1 without gelatiniza- 

 tion ; the solution freed of silica yields little or no precipitate with 

 ammonia (Al) (those containing iron will yield a brown precipi- 

 tate) ; the filtrate tested with sodium phosphate shows magnesium. 



General description. Massive with a microscopic fibrous or 

 felted structure, also foliated or slaty. Chemically serpentine is a 

 basic orthosilicate, which when fused breaks down to olivine and 

 enstatite. Iron may replace the magnesium to as much as seven 

 per cent, and also manganese or nickel in small quantities. It is 

 in all cases a secondary product formed by the weathering and 

 hydration of a large number of minerals ; in fact, any silicate con- 

 taining considerable magnesium may form serpentine. It is 

 especially derived from the weathering of olivine, tremolite, and 



