JULIEN, DETERMINATION OF MINERAL CONSTITUTION 133 



The following is presented as a good example, on the one hand, of the 

 deceptive appearance which may be assumed by a chemical analysis, and, 

 on the other, of the corrective evidence supplied by optical examination of 

 the same specimen. 



" Marmolitic antigorite." 



From New Idria, California. Pale apple-green. Analysis by G. F. 

 Becker, who states: "In pure serpentine 40.42 per cent, of magnesia cor- 

 responds to 41.52 per cent, of silica. It appears therefore that this mineral 

 is in fact a serpentine comparatively free from impurities. When reduced 

 to the proper thinness it was found that the material was far from homo- 

 geneous. A portion as seen under the microscope appeared absolutely 

 colorless by transmitted light, while the remainder was of yellowish and 

 brownish tints, in spots almost opaque, although by reflected light this posi- 

 tion retained the pale apple-green color of the hand specimen .... clouded 

 by the presence of extremely microcrystalline particles" (Mon. U. S. Geol. 

 Surv., XIII, 1888, 110). 



" Antigorite." 

 From Antigorio, Piedmont. Analysis by Kenngott. 



