452 L. G. Eakins — Two Sulphantimonites from Colorado. 



This mineral, it is seen, fills a place in the group — 3RS, 

 2(As, Bi, Sb) 2 S 3 , of which there are but few good examples, and 

 which until now has not had an antimony representative. 



The somewhat low summation of the analysis is probably due 

 to two causes ; first, a small amount of soluble gangue which 

 was present and undetermined ; second, the sulphur is about 

 four-tenths of one per cent less than required, due to the slight 

 natural oxidation of the mineral together with an additional 

 amount induced by treatment with dilute hydrochloric acid for 

 the removal of calcite. In addition to the complete analysis 

 given, there were additional determinations made of lead, an- 

 timony and sulphur, the results obtained being in strict agree- 

 ment witli those given above. 



The second of these sulphantimonites was collected in the 

 summer of 1887, by Mr. Whitman Cross ; it comes from a mine 

 on Augusta Mountain, Grunnison Co., Col., this locality being 

 about one mile east of the " Domingo " mine. 

 | JLocally this mineral is also known as " mineral wool," and 

 although differing considerably in appearance from the one just 

 described, they were, on account of the similarity of occurrence, 

 considered as probably identical. 



It occurs in a siliceous gangue together with pyrite and sphale- 

 rite, and forms groups of acicular crystals which are elongated 

 prisms, deeply striated ; but whose form could not be deter- 

 mined. 



The individual crystals of this mineral are considerably larger 

 than those of the one previously described, and in conse- 

 quence they do not tend so much to form matted aggregates. 

 Its color is a bright, steely, grayish black, with no tendency 

 toward tarnish or iridescence. The separation of this mineral 

 from the accompanying ones and the gangue, was a matter of con- 

 siderable difficulty ; on account of their size the crystals could 

 not be successfully washed out from the other material, but by 

 the use of a rapid current of water, and the Thoulet method, 

 a small quantity was finally procured perfectly free from every- 

 thing except some pyrite, and that had no effect upon the 

 analysis, as the mineral was dissolved in a mixture of hydro- 

 chloric and tartaric acids, leaving the pyrite unattacked ; it was 

 then filtered through a Grooch crucible, and the amount of py- 

 rite determined and deducted from the material taken. The 

 fact that but a trace of iron was found in the analysis is con- 

 clusive proof that the pyrite was practically unattacked. 



Blowpipe characteristics are the same as in the one before 

 described. 



The analysis is as follows : 



