168 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



and Bobbie Anderson, and in all of these veins it seems to be prac- 

 tically nonargentiferous. Similar silver-free tetrahedrite has also 

 been noted in small amount in the ore of the Wisconsin claim east of 

 Kellogg, where it is later than the quartz-ankerite-pyrrhotite minerali- 

 zation in which it fills seams. 



WASHINGTON COUNTY 



The silver-bearing ores of the Mineral district, chief among which 

 are the Silver Bell, Maria, and Black Hawk, with numerous lesser 

 prospects, all contain notable amounts of tetrahedrite associated with 

 galena, sphalerite, pyrite, etc. 53 



TENNANTITE (149) 



Copper sulpharsenite, 5Cu 2 S. Isometric, tetrahedraL 



2 (Cu,Fe,Zn)S. 2As 2 S 3 . 



BEAR LAKE COUNTY 



Tennantite, like tetrahedrite, is commonly known as gray copper. 

 The two minerals are very similar in all their properties, the principal 

 difference being in the relative proportions of arsenic and antimony, 

 those containing arsenic in excess of antimony being classified as 

 tennantite. A "gray copper" from the Humming Bird mine, in 

 Paris Canyon near Paris in the St. Charles district, contains more 

 arsenic than antimony and hence is referable to tennantite. 530 The 

 mineral, which is massive, occurs in a breccia composed of quartz 

 and jasper and is partly altered to azurite and malachite. It is quite 

 possible that, v/ere the gray copper ores from all localities in the 

 State submitted to a careful chemical examination more of them 

 would be found to be predominantly arsenical. 



STEPHANITE (153) 



Silver sulphantimonite, 5Ag 2 S.Sb 2 S 3 . Orthorhombic, hemimorphic. 



The black silver mineral commonly known as antimonial silver or 

 brittle silver has been a prominent ore mineral in much of the high- 

 grade silver ore mined in the State. 



BLAINE COUNTY 



In the Lava Creek district stephanite occurs as small disseminated 

 grains in quartz and intergrown with pyrite and also with proustite 

 in veinlets cutting the sulphide ore. 54 



" Waldemar Lindgren. U. S. Geol. Survey, 22d Ann. Rept., pt. 2, pp. 754-755, 1901. 

 «• R. W. Richards. U. S. Geol. Survey, Bull. 470, p. 179, 1911. 

 " J. B. Umpleby. U. S. Geol. Survey, Prof. Paper 97, p. 123, 1917. 



