TETRAHEDRITE, TENNANTITE, AND NACRITE, 



OP THE KELLOGG MINES OF AKKANSAS. 



A short time since Prof. E. T. Cox, of Indiana, sent to me an 

 antimonial copper-ore containing silver, one fragment being 

 the termination of a crystal having a number of small but 

 beautiful faces ; another was a minute crystal of a different 

 form. In the hands of Prof. Cox a blowpipe analysis had 

 given about five per cent, of silver in some of the mineral. 



The crystalline fragments were first examined, and they 

 enabled me clearly to trace out tetrahedrite in one and ten- 

 nantite in the other. The faces on the tetrahedrite were small, 

 but beautiful and very numerous ; from the number on the 

 fragment examined there would not have been less than from 

 sixty to seventy had the crystal been perfect. It corresponds 

 very nearly to the crystal figured in Dufrenoy's Mineralogy, 

 plate 124, fig. 441, which he speaks of as coming from Moschel- 

 landsberg, a locality that I am not able to discover. Good 

 measurements were made on a few of the faces. 



P on P 70°: P on b s 159° 3(K; P on a 2 144° 30'. 



Specific gravity of different specimens varied from 4.78 to 



5.08 ; the latter was the specific gravity of the above crystal. 



The analysis of two specimens, No. 2 being a part of the 



crystal, gave 1 2 



Antimony 26.50 27.01 



Sulphur 26.71 25.32 



Copper 36.40 33.20 



Iron 1.89 .82 



Zinc 4.20 6.10 



Silver 2.30 4.97 



Arsenic 1.02 .61 



99.02 98.03 



The quantity of No. 2 analyzed did not exceed three hun- 

 dred milligrammes. 



There are two minerals, consisting of minute micaceous 

 scales, on the quartz containing this gray copper. One of them 



