THE LESSER METALS. 261 



bismuth minerals, and not a few other places in the country con- 

 tain traces, but the San Juan is the only serious one as yet. 1 



CHROMIUM. 



2.14.11. Chromite, whose theoretical composition is FeO.Cr 2 O 3 , 

 with Cr. 2 O 3 68#, often has MgO and Fe 2 O 3 replacing its normal 

 oxides. The percentage of O 2 O 3 is thus reduced. It is always 

 found in association with serpentine, which has resulted from the 

 alteration of basic rocks consisting of olivine, hornblende, and 

 pyroxene. These minerals contain the chromic oxide probably as 

 a base in their fresh condition, but lose it on alteration. A chrome 

 spinel, picotite, which is an original mineral in these rocks, likewise 

 affords it. The chromite is scattered through the serpentine, often 

 forming masses of large size. Traces of nickel minerals are fre- 

 quently noted associated with the chromite. 



2.14.12. Example 49. Disseminations of chromite in serpen- 

 tine. Pennsylvania and Maryland. Great areas of this rock are 

 found in southeastern Pennsylvania and in the adjacent parts of 

 Delaware and Maryland. Considerable mining has been done in 

 the past. \Voods mine, in Lancaster County, Pennsylvania, has 

 furnished great quantities, and other large producers are situated 

 in the Bare Hills, near Baltimore. This section is now no longer 

 commercially productive. Chromite has also been announced 

 from several places in the South, no one of which has yet sent 

 notable quantities to the market. 



2.14.13. California. As already mentioned under the precious 

 metals, great areas of serpentine occur on the western flanks of 

 the Sierras and in the Coast range. In Del Norte, San Luis Obis- 

 po, Placer, and Shasta counties, California, they furnish commer- 

 cial amounts of chromite. In some places the ore is followed by 

 underground mining, and in others it is gathered as float material. 

 The irregular distribution, always characteristic of the mineral, 

 renders underground work uncertain. Good ore should afford 50^ 

 Cr 2 O 3 , and in California no ore less than 47# is accepted. It 

 brings in the East $22 to $35 per ton. Considerable quantities 

 are imported. 2 



1 Mineral Resources of the U. ., 1885, p. 399. B. Silliman, " Bismuth- 

 inite from the Granite District, Utah," Amer. Jour. Sci., iii., VI. 123. 

 H. L. Wells, " Bismuthosphaerite from Willimantic and Portland, Conn ," 

 Amer. Jour. Sci., iii., XXXIV. 271. 



2 F. D. Chester, Ann. Rep. Penn. Survey, 1887, p. 93, describes the 



