THE MINERALS OF IDAHO 47 



mines, under the same conditions and of about the same quality as 

 those in California. Some excitement has occasionally arisen about 

 these Idaho diamonds. In 1864 to 1866 local and mining papers 

 made many references to reported or anticipated discoveries; but 

 nothing of any importance was found. In the winter of 1892-93 

 the matter again attracted some attention. Only small quartz crys- 

 tals and no diamonds were found, the name "Diamond Basin" having 

 given color to the reported findings. Diamond Basin lies on the Snake 

 River in Owyhee County. The excitement, intense for a time, sub- 

 sided before the winter was over. 4 



It is possible that a few small diamonds may occur in placers in 

 other portions of the State, but the possibility of deposits of stones of 

 gem quality being found is very remote. The source of the Rock 

 Flat crystals is not known, but the fact that chromite and a trace of 

 platinum have been reported from the same claim may indicate their 

 derivation from a small intrusive mass of peridotite. Scattered 

 stones have been found from time to time in the gold placers of Cali- 

 fornia, but no diamond deposits have been found in that State in 

 which the geological environment is, on the whole, much more 

 favorable for the occurrence of this mineral. 



GRAPHITE (2) 



PLUMBAGO, BLACK LEAD 

 Carbon, C. Hexagonal. 



The black hexagonal form of carbon, graphite, is not abundant in 

 Idaho and no deposits of commercial importance are known there. 

 The most common occurrence of this mineral is as a very finely dis- 

 seminated coloring matter in slaty rocks in various parts of the State 

 as, for example, the Prichard formation in the Coeur d'Alene district 

 and the ore-bearing Devonian slates of the Wood River district in 

 Blaine County. 



ADAMS COUNTY 



Graphite has been mentioned as occurring in the Seven Devils 

 district as a minor constituent of the ores in some of the contact- 

 metamorphic copper deposits. 



BLAINE COUNTY 



Some attempt has been made at exploring certain graphite-rich 

 streaks in the graphitic slates of the Devonian formation on Trail 

 Creek at the town of Ketchum on upper Wood River. The claims 

 opened by Messrs. Hampton and Griffith in 1908 and a small pro- 

 duction of amorphous graphite was reported in 1909 but nothing 

 since. 5 



4 George F. Kunz, Precious stones. U. S. Geol. Survey, Mineral Resources for 1892, p. 759. 

 « U. S. Geol. Survey, Mineral Resources, 1913, pt. 2, p. 199. 



