Alteration Products from the Black Hills, S. D. 107 



The ratio of the sulphur required by the tin as stannic sulphide 

 to the total sulphur is as 1 : 2'16 or 1:2 giving us the formula 

 2RS + SnS 2 in which R=-Cn^, Fe M , Zn + Cd M , which agrees 

 with the formula heretofore accepted for stannite except that 

 a small portion of the zinc in this specimen has been replaced 

 by cadmium. 



I have been very explicit in describing the mass from which 

 I obtained this portion of stannite for the reason that about 

 four years ago I found a similar earthy material occurring in 

 patches in the coarse-grained granite of the Etta Mine. I suc- 

 ceeded in obtaining small quantities of this material at various 

 times and finally enough for an analysis. The quantity 

 actually obtained was rather more than 0*5 grm. 



Whether it occurs more abundantly at some point in the 

 workings which I have failed to find, I cannot say, but I found 

 it occurring very sparingly. The chief portion of all that I 

 obtained on my various visits to the locality extending over a 

 period of two years was found scattered in small bunches 

 through a large piece of granite which had been removed from 

 its place and carried some distance from the mine. The point 

 at which I found it most abundant in place was in the face of 

 an open cut on the northeast side of the hill together with 

 cassiterite ; they are intimately associated with a somewhat 

 laminated feldspar. I have reason to believe that it was more 

 abundant formerly than now, as I came into possession of a 

 specimen taken from the mine, under its first management, 

 which is much richer in this material than any specimen which 

 I have myself been able to find or to subsequently obtain. The 

 association of this material with the cassiterite is more inti- 

 mate in this specimen than is usual ; in only one instance have 

 I seen it more so, namely in a piece of massive cassiterite 

 which has a small depression partly filled with it inclosing 

 fragments of stannite. This is interesting because the speci- 

 men was found at the point where this cut was opened, and 

 establishes the identity of the Etta and Peerless material so 

 far as their origin is concerned. An analysis of the best Etta 

 material that I could obtain was made in 1889 and is given 

 here for comparison with one of Peerless material which was 

 made recently. The air-dried material had a dirty green color 

 and gave, after deducting 9*84 per cent gangue : 



Atomic equivalents. 



H n 



13-87 



H -0154 



15-40 



14-66 



29-3 



30 



CuO 



12-53 



Cu -1021 



1-615 



1-44 



2-88 



3 



Fe 2 3 



8-94 



Fe -0626 



1-119 



1 



2 



2 



SnO n 



64-33 



Sn -5061 



4-289 



3-83 



7-66 



8 



S0 3 



trace 



O -3105 



19-400 



17-38 



34-76 



35 



Sb 2 5 

 ZnO 



trace 

 trace 













0-9967 











99-6' 



