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GEOLOGY. — Strontianite deposits near Barstow, California. Adolph 

 Knopf. U. S. Geological Survey Bulletin, 660-1. Pp. 14. 1918. 



Strontianite in economically important quantity has recently been 

 found near Barstow, San Bernardino County, California. The for- 

 mation in which the deposits occur consists of a series of lake and 

 terrestrial beds of Upper Miocene age. A threefold subdivision of 

 the beds may easily be recognized. The strontium deposits are re- 

 stricted to the middle subdivision, which is made up chiefly of grayish- 

 green clay in thick beds. In places reefs of algal limestone are promi- 

 nent, and obviously this part of the formation was laid down in a lake. 



Strontianite and strontium-bearing rock have been found at a large 

 number of places in a belt about 2 miles long. They occur as layers 

 that lie parallel to the bedding of the inclosing clays and are distrib- 

 uted at intervals through a thickness of several hundred feet. The 

 strontianite occurs in two forms — as fibrous masses of resinous color 

 and luster and as dense, exceedingly fine grained gray or drab material, 

 which in appearance exactly resembles limestone. The two varieties 

 occur separately as a I'ule, but in some deposits they are intermingled, 

 spherulites of coarse resinous strontianite being irregularly scattered 

 through gray aphanitic strontianite rock. Some celestite is present in 

 the lower-grade material of the district. 



The thickest body of pure spherulitic strontianite that had been 

 found at the time of visit is 14 inches thick, but the gray aphanitic 

 strontianite rock had been found in layers as much as 3 feet thick. 



The strontianite deposits were formed by the replacement of the 

 lacustral limestone beds that are interstratified in the clays. They 

 thus differ widely from the only other commercially productive stron- 

 tianite deposits — those of the Miinster district, Westphalia — which 

 consist of a series of steeply inclined veins cutting horizontal marine 



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