Ti:ST.S OF SERPENTINE. 



Ill 



tion as seen under tlie microscope appeared absolutely colorless by trans- 

 mitted liglit, while the remainder was of yellowish and brownish tints, in 

 spots almost opaque, although by reflected light this portion retained the 

 pale apple-green color of the hand specimen. Tlie more liighly colored 

 portions of the slide appear to be clouded by the presence of extremely 

 microcrystalline particles, perhaps ferric oxide; but these particles can 

 hardly have any direct connection with the more brilliant colors of polari- 

 zation, for the portions containing them, when in proper relation to the 

 uicols, extinguish liglit almost as completely as the others. 



The entire slide has a banded structure, occasioned by the arrange- 

 ment of fibers, which is similar in character to that most usual in the ser- 

 pentine of the Coast Rang'es, though more simple. The colorless portion 

 between crossed nicols varies from black to light gray, and the brilliancy 

 of the tints increases with the coloration, being yellow in certain positions 

 where the mass is lightly colored and red where the color in natural light 

 is more intense. Precisely the same relation was observed in slides from 

 other localities and of all degrees of impurity. 



For comparison two serpentines from Sulphur Bank (Nos. 18b and 

 78e) were analyzed. The former is a nearly black, impure-looking mass, 

 through which are distributed foils similar to those of bastite, excepting 

 that they lack the metallic luster. Under the microscope it was found to 

 contain, besides much opacite, serpentine polarizing in yellow tints, though 

 the preponderating mineral shows gray interference colors. No. 78e is a 

 light-green mineral from the same locality as that last mentioned, but 

 much purer in appearance. 



Dark 



serpentine. 



Water, H'O 



Silica, SiO' 



Alumina, AlW 



Chromic oxide, C r-0' . . . 



Ferrous oxide, FeO 



Xickel oxide, KiO 



Manganous oxide, MuO 

 Magnesia, MgO 



13.81 

 39.64 

 1.30 

 0.29 

 7.76 

 0.33 

 0.12 



Light 

 serpentine. 



14.16 

 41.86 

 0.69 

 0.24 

 4.15 

 Trace 

 0.20 

 38.63 

 99.93 



