A NEW OCCURRENCE OF CRISTOBALITE IN 

 CALIFORNIA 



AUSTIN F. ROGERS 

 Stanford University, California 



Cristobalite, one of the rarer high- temperature forms of silica, 

 was first described from the andesite of Cerro San Cristobal, near 

 Pachuca, Mexico, by vom Rath,^ and was established as a distinct 

 mineral species by Mallard.^ Artificial cristobalite has been pre- 

 pared in the Geophysical Laboratory at Washington and its proper- 

 ties and its relation to the other forms of silica have been studied 

 by Fenner.3 Silica bricks are made up of artificial cristobalite and 

 tridymite, and so these minerals are of some importance to the 

 metallurgist. 



The work of the Geophysical Laboratory is extremely valuable, 

 but of especial interest to the mineralogist and petrographer is the 

 actual occurrence of these minerals in nature. The laboratory 

 production of such artificial minerals is largely to aid in the inter- 

 pretation of natural occurrences. Cristobalite has been known 

 from five or six foreign locahties for some time and in 1918 the 

 writer'' described it from two American localities, both in California. 

 Since that time he has obtained specimens from five additional 

 American localities. 



The cristobaHte described in this paper, like the Yellowstone 

 Park occurrence recently described,^ is found in a rhyolitic obsidian. 

 The exact locality of the specimens could not be ascertained. The 

 material was placed in the writer's hands by Mr. R. M. Wilke, 

 mineral dealer of Palo Alto, California. Mr. Wilke obtained the 

 specimens from a prospector, who would not divulge the locality. 

 Mr. Wilke, however, says "I am sure the place is somewhere in the 



' Neiies Jahrb. Min. (1887), pp. i, 198. 



""Bull. Soc. Min. France, Vol. XIII (1890), p. 172. 



^Amer. Jour. Sci. (4), Vol. XXXVI (1913), pp. 331-84. 



'^Ibid., XLV, pp. 222-26. 



^ Amer. Mineralogist, Vol. VI (1921), pp. 4-6. 



