Palache — Notes on Tellurides from Colorado. 419 



Art. XL. — Notes on Tellurides from Colorado ; by 

 Charles Palache. 



1. Sylvanite from Cripple Creek. 



The presence of sylvanite among the telluride ores of 

 Cripple Creek was first made known by the analysis of Pearce,* 

 and the considerable silver content of the ores was credited by 

 him, in large part at least, to that mineral. His analysis how- 

 ever was made on massive material, and the lack of crystallo- 

 graphic evidence of the presence of sylvanite, together with 

 the failure of other investigators to find the mineral, led to 

 some mistrust of his results and the silver content of the ores 

 was doubtfully attributed to the common ore, calaverite, which 

 was known to carry a small percentage of silver. 



Of recent years, however, crystallized sylvanite appears to 

 have been found in considerable amount in several of the 

 Cripple Creek mines and it is the purpose of this paper to 

 describe a series of sylvanite crystals which offer most satisfac- 

 tory proof of the correctness of Pearce's original conclusion. 



The crystals to be described were placed at the writer's dis- 

 posal for examination by Professor Hobbs of the University of 

 Wisconsin, to whom they had been presented by Mr. F. M. 

 Woods of Victor, Colorado, the collector. The crystals were 

 in two lots labelled respectively : " Sylvanite," Mabel M. 

 Property, Beacon Hill, Victor ; and " Calaverite," Victor, Col. 



All proved to be alike sylvanite and consisted of isolated 

 crystals and crystal fragments varying in size from l mm to 8 mm 

 in greatest dimension. The color is pure silver-white and 

 many of the fragments display the perfect cleavage parallel to 

 the clinopinacoid which is characteristic of this mineral and 

 -serves well to distinguish it from the more common calaverite. 

 The specific gravity, determined on three isolated crystals on 

 the hydrostatic balance, was 8*161. 



The dominant habit of the crystals is thin tabular parallel to 

 h, 010, the edges of the tables being bounded by planes of the 

 orthodome zone. The tables are frequently as thin as paper 

 and the edge planes become too small to be measurable. A 

 second well-marked habit is prismatic, determined by the pro- 

 nounced development of the zone of the positive unit pyramid 

 and orthodome, (111) and (101), and other pyramids of this 

 zone. As will be seen from the figures, crystals of this habit 

 are frequently rich in forms, some of which proved to be new 

 to the mineral. 



*Proc. Colo. Sci. Soc, 1894. 



