F. W. Clarke— Some NicJcel Ores from Oregon. 487 



of genthite, together with the maimer in which the arms grad- 

 ually fade away into the serpentine at once suggests the source 

 from which the genthite has been drawn. The genthite and 

 serpentine are thoroughly intermingled, but the former is gen- 

 erally present in such small 

 quantities as to be overlooked un- 

 less it is the object of special 

 research. It occurs in the ser- 

 pentine directly connected with 

 the grains of olivine from 

 which the serpentine has been 

 derived, and there is every rea- 

 son to believe that the genthite 

 came from the same source." 



In order to secure completer 

 confirmation of the idea that 

 the nickel of the greater silicate 

 deposits is derived from the 

 alteration of nickeliferous olivine, Mr. Diller at my request, 

 also examined specimens from Webster, 1ST. C, and from New 

 Caledonia. Concerning the Webster genthite Mr. Diller re- 

 ports that "it is almost identical with that from Oregon, ex- 

 cepting that it is not so thoroughly intermingled with quartz. 

 The relation of the genthite to the serpentine and the olivine 

 at the Webster locality is exactly the same as at Riddle. The 

 rock at Webster differs slightly from that at Riddle in 

 containing a smaller proportion of enstatite, and belongs to 

 the peridotites to which the name 'dunyte' has been ap- 

 plied " He also finds the New Caledonia mineral to be iden- 

 tical with genthite in its physical properties, and says — 

 "Under the microscope it varies from pale yellowish green 

 to light coffee-brown, and is either completely isotropic or 

 exhibits only faint aggregate polarization. Like the genthite 

 of Oregon it is deposited in layers and cavities thoroughly 

 intermingled with quartz, and in the same thin section may be 

 seen serpentine with traces of olivine and enstatite so disposed 

 as to clearly indicate that the serpentine, noumeaite, and other 

 secondary products have resulted from the alteration of perido- 

 tite." This observation confirms the earlier one of Des Cloi- 

 zeaux (1. c), who stated that the noumeaite was imbedded in a 

 serpentine rock which appeared to be derived from olivine, and 

 which contained crystals of the latter mineral plentifully dis- 

 seminated through it. A similar suggestion is made by Mr. 

 H. J. Riddle,* who regards the nickel of the Webster deposits 

 as an original constituent of the olivine rock, and cites an ex- 

 periment of Mr. G-. B. Hanna, who found 0*15 per cent of 

 nickel oxide in a chrysolite from Waynesville, 1ST. C. 

 * Mineral Resources of the U. S., 1886. 



