106 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



STROMEYERITE (55) 



Silver-copper sulphide, Ag 2 S.Cu 2 S. Orthorhombic. 



The occurrence of stromeyerite in the State has in no case been 

 definitely established. Sectile grains of a mineral resembling argen- 

 tite but assuming a bluish tarnish upon exposure which react quali- 

 tatively for silver, sulphur, and copper occur frequently in rich silver 

 ores and are probably stromeyerite. 



ELMORE COUNTY 



Some of the richest ore from the Atlanta mine, Atlanta district 

 (Cat. No. 30199, U.S.N.M.), composed of large masses of granular 

 pyrargyrite and stephanite contains disseminated blue-tarnishing 

 grains of this supposed stromeyerite associated with dull mossy 

 black argentite. 



OWYHEE COUNTY 



In ore from the Rising Star mine soft gray grains up to 3 milli- 

 meters in diameter become deep blue upon exposure. These grains, 

 which are probably stromeyerite, are disseminated in quartz with 

 stibnite, stephanite, argentite, and polybasite. 



SHOSHONE COUNTY 



A single specimen of very rich silver ore from the Caledonia mine, 

 Coeur d'Alene district, consists of white quartzite fragments cemented 

 by a dark gray sectile mineral which tarnishes to a purple color. 

 This gray mineral, which contained disseminated grains of chalco- 

 pyrite, showed on analysis silver, copper, and sulphur, and was no 

 doubt stromeyerite. 



SPHALERITE (58) 

 Zinc sulphide, ZnS. Isometric, tetrahedral. 



Sphalerite, the sulphide of zinc, is a very common mineral, being 

 the only important ore of zinc in Idaho and also occurring, like galena 

 and pyrite, in numerous veins as an accessory. This mineral, which 

 is almost always massive with coarse to fine granular structure, passes 

 in many places under quite a variety of names, such as zincblende, 

 black jack, rosin jack, etc. These names are not so commonly 

 applied in Idaho where the prevailing type of sphalerite is very dark 

 brown and is known simply as "zinc." The mineral varies in color 

 however, from nearly white through various shades of yellow and 

 amber or occasionally green to dark brown and black, the latter color 

 being due to some iron being present in isomorphous form. In a 

 majority of cases the sphalerite is a more or less valueless and trouble- 

 some constituent of the' ores, although in recent years the mineral 

 has been marketed in large amounts, especially from the Coeur 

 d'Alene region. Here it usually occurs mixed with galena from which 



