G-enth.] ^^^ [Aug. 21, 



At the latter locality it is found in sugary quartz associated with gold, 

 galenite, chalcopyrite, pyrite, antimonial tetrahedrite, and more rarely 

 with nagyagite and a greenish micaceous mineral resembling fuchsite. 

 It occurs in small quantities only, and is so much mixed with the other 

 minerals, that I was unable to select enough for a quantitative analysis. 

 It is easily recognized by its tin-white color, with the greenish-yellow 

 hue, and its great lustre. It is found in particles showing the distinct 

 cubical cleavage, but also finely granular. A very interesting but quite 

 small piece shows a cleavage mass, pai^t of which is altaite, part galenite, 

 without any interruption in the cleavage plane, both minerals being 

 easily distinguishable by their color. 



The altaite at the Red Cloud Mine, Colorado, is found in larger masses, 

 generally, however, very much intermixed with other minerals, espe- 

 cially native tellurium and sylvauite. It is associated with pyrite, siderite 

 and quartz. Sometimes it is found in indistinct cubical crystals, appar- 

 ently coated with a thin film of galenite ; rarely in larger cleavage masses. 

 I have a cleavage cube of | of an inch in size of distinct cleavage : some 

 of the planes are slightly coated with galenite. The most frequent occur- 

 rence is that in gi-anular masses with indistinct cubical cleavage, a frac- 

 ture inclining to subconchoidal and a yellowish tarnish.* 



The analysis of a portion of the cleavage cube gave the following 



results : 



Spec. Gr. = 8.060 



Quartz = 0.19 — 0.32 



Gold = 0.19 — 0.16 



Silver ^ 0.62 — 0.79 



Copper = 0.06 — 0.06 



Lead = 60.22 — 60.53 



Zinc = 0.15 — 0.04 



Iron = . 0.48 — 0.38 



Tellurium = ' 37.99 — 37.51 



99.90 99.74 



4. Hessite, Auriferous Hessite, Petzite. 



Varieties of telluride of silver with variable quantities of gold are the 

 principal minerals which give the ores of the Red Cloud Mine their value. 

 I believe that I was the first to whom specimens of the rich auriferous 

 variety were sent by Mr. Schirmer. These I have determined as petzite. 

 Prof. Silliman mentions a variety (1. c.) containing 7.131 per cent, of gold 

 and 51.061 per cent, of silver, of which he gives a very accurate descrip- 

 tion ; he evidently had only this one, and therefore comes to the conclu- 

 sion that the Red Cloud Mine contained no other vax'ieties. It will be 



* In Dr. Burkart's paper (I.e.) p. 487, line 12 from the bottom, read: Iiexaedrische 

 instead of hexagonale. 



