from Mollie Gibson Mine, Aspen, Colorado. 17 



Massive mineral. 

 Analysis by S. H. Pearce. 

 Specific gravity of three pieces 

 606, 5-92 and 6' 10. 



I. II. Average. 







Crystals from siderite. 

 Analysis by S. L. Penfield. 

 Specific gravity 6'080. 



S 15-77 



15-88 



15-83 









S 



17-42 



As 4-48 



4-46 



4-47 









As 



6-10 



Sb 0-13 





0-13 









Sb 



0-26 



Ag 42-52 



42-45 



42-49 









Ag 



49-51 



Cu 9-21 



9-15 



9-1S 









Cu 



12-92 



Zn 2-23 



2-27 



2-25 









Zn 



2-45 



Pb 2084 



20-82 



2083 = 



galena. 



PbS 



24-05 



Pb 



1058 = PbS 12-22 



FeCOs 2-57 



2-57 



2 57 "j 









FeCOs 



0-46 > 0-59 

 3 0-13 f °° J 



MnCC-3 0-9S 



107 



103 1 



0-20 f 







4-13 



MnCO 



CaCOs 0-20 















Insol. 0-32 



■34 



0-33 J 



99-31 



Impi 



irity 











28-18 



99 83 Impurity 12 'SI 



The above analyses do not agree, nor in their present form 

 can they be referred to any known species, but after deducting 

 28-18 per cent of impurities from the first and 12-81 from the 

 second, and recalculating to one hundred the results are as 

 follows : 



Crystals from siderite Theoretical composition where 

 Sp. gr. corrected =5 94 Ag 2 : Cu 2 : Zu = 263 : 117:43 



18-13 Ratio 18-13 



7*01 -J- 150 =-0467) _,>._ 7-08 



-04/9 



Massive 



mineral. 



s 



17-73 



As 



6"29 



Sb 



0-18 



Ag 



59-73 



Cu 



12-91 



Zn 



3-16 



0-30-=-244 =-0012 



56-90H-216 = -263 ) 57'07 



14-85H- 126'8== M17 [••423 14-91 



2'81-J- 65 = -043 \ 2-81 



100-00 100-00 100-00 



The analyses are now similar and in the second, which was 

 made on the purest material, the ratio of (Ag 2 + Cu 2 +Zn) : 

 (As 2 +Sb 2 )=-423:-0479 or 9-00:1-02, almost exactly that re- 

 quired by the formula 9Ag 2 S, As 2 S 3 . As is always the case 

 with this mineral, a rather large proportion of the Ag 2 has been 

 replaced by Cu 2 and some by Zn. The analyses are also 

 interesting as showing that this mineral is a nearly pure arsen- 

 ical polybasite. H. Rose* gives one analysis of a variety 

 from Chemnitz in Saxony, which agrees with ours in contain- 

 ing only a trace of antimony ; with this exception, in all of the 

 analyses which have been published, antimony predominates. 

 Although polybasite has been known to occur in the United 

 States, the only published analysis is one by F. A. Genthf of 

 a crystal from the Terrible Lode, in Clear Creek Co., Colorado. 



* Pogg. Annalen, xxviii, 1833, p. 156. 



f Proc. Ame;- Phil. Society, xxiii, 1 886, p. 39. 



Am. Jour. Sci.— Third Series, Vol. XLIV, No. 259.— July, 1892. 

 2 



