188 Genth and Penfield — Contributions to Mineralogy. 



Si0 o 33-33 



Al o 3 0-70 



CaO 0-49 



Fe 0-16 



Cu trace 



Pb 1-21 equivalent of Te 0-75 



Ag 39-42 " " 23-38 



Te 25-53 



Se trace 24-13 



100-84 



This would represent: 62 - 80 per cent Ag 2 Te, 1-96 per cent 

 PbTe with 1*40 per cent of tellurium, which may be present 

 as native tellurium or perhaps as tellurous oxide. The presence 

 of some incrustations, resembling tellurite, would indicate that 

 the latter supposition is probably the correct one. 



3. Bismutite. 



Associated with the phenacite of Mount Antero in Chaffee 

 County, Colorado, are quartz, orthoclase, scales of muscovite, 

 hematite, and a grayish or yellowish green bismuth mineral in 

 prismatic form. The hematite occurs in small brilliant crys- 

 tals, the largest not over ■^ [nm broad and about l-5 mm thick, the 

 combination being short prisms terminated by a flat rhombo- 

 hedron. Of the bismuth mineral only one fragment of a crys- 

 tal was observed of a darker greenish color and having angles 

 agreeing with the sulphide Bi„S 3 , from the alteration of which 

 it probably had been derived. Other small crystalline masses 

 were observed, resembling bundles of deeply striated crystals, 

 the largest about 30 mm in size, but, unfortunately, throughout 

 the whole mass, contaminated with salts of lead, copper, zinc, 

 ferruginous clay, etc. Examining the association it appears 

 that quartz, muscovite in hexagonal plates and hematite are 

 the oldest, after which the bismuth mineral was deposited, and 

 upon this, the most recent phenacite, which frequently is 

 found upon the bismuth mineral and between its fissures, — or 

 the phenacite has crystallized around fragments of the same. 



It was impossible to obtain the bismuth mineral in a state of 

 purity. The best gave the composition given below, after 

 deducting in analysis I, 5*11 per cent of impurities, such as 

 hematite, muscovite and ferruginous clay — in analysis II, 4 22 

 of the same. 



The sp. gr. of the material for analysis was found to be : 

 6-293, while the darker greenish crystal yielded : 7-330. The 

 analyses gave : 



