376 A. H. Chester — Krennerite from Colorado. 



of krennerite rather than of calaverite, the crystals of which do 

 not decrepitate when heated, have no basal cleavage, and accord- 

 ing to Penfield,* are probably triclinia The crystals now 

 described occur on a quartzite gangue, and are partially imbed- 

 ded in a thin layer of soft, gray material, which may be kao- 

 linite, but has not yet been examined. ' Small crystals of pyrite 

 are scattered abundantly through the quartzite gangue. 



The chemical examination has been made by my colleague, 

 Prof. W. S. Myers. Three of the crystals were carefully 

 detached, and when cleared as far as possible of all adhering 

 matter, until nothing but crystalline faces could be observed 

 under the magnifier, afforded extremely pure material, as 

 shown by the analysis, the results of which are as follows, 

 tellurium being estimated by difference : 



Au 43-33 per cent. 



Ag.. 0-45 " 



[Te] 55-01 



Insoluble --- 1'21 " 



Fe.O, -- trace. 



'3 3 



Deducting the insoluble matter and calculating to one hun- 

 dred we have, 



Per cent. Ratio. 



Au .-- 43-86 "223 \ 



Ag 0-46 -004 \ ll1 1UU 



Te 55-68 -445 1-97 



The ratio of Au + Ag : Te is very nearly 1 : 2, which gives for 

 the formula of the mineral AuTe 2 , the same as in calaverite and 

 sylvanite, though with less silver than has been recorded here- 

 tofore. In this group, however, variations in the amount of 

 silver are very wide, and there is probably no fixed proportion 

 of silver to gold. The present analysis corresponds very 

 closely with that of calaverite from the same locality, by 

 Hillebrand,f and it is very desirable that more crystals of cala- 

 verite should be found to settle the question positively as to 

 its crystalline form, for if it is triclinic we have three distinct 

 tellurides of gold and silver, orthorhombic krennerite, mono- 

 clinic sylvanite and triclinic calaverite. But it seems more 

 probable that there are only two of these minerals and that 

 calaverite is the silver-free form of sylvanite; for this new 

 analysis, of undoubted krennerite, varies as widely from the 

 earlier ones in its proportion of silver as do the analyses of 



*This Journal, III, 1, 131, 1895. 

 fThis Journal, III, 1, 128, 1895. 



