206 Hough — An Unlisted Mineral. 



Art. XV. — Notes on an Unlisted Mineral; by George 



J. Hough. 



In 1901 there was found in a famous old mine in 

 Mexico, a small amount of an unknown silver-copper min- 

 eral; I made reference to the discovery of this mineral 

 in a descriptive article on Mexican Mines, published in 

 the Mining and Scientific Press in 1911, but did not 

 describe it in detail. The mineral was found in the Coci- 

 nera Mine of the Mexican Copper Company, at Ramos in 

 the State of San Luis Potosi; a place famous in the old 

 colonial days of Mexico as a silver producer. 



The ore body in this mine, from the earliest times, was 

 largely composed of heavy copper sulphide minerals, 

 notably bornite and tetrahedrite ; but at a depth of 1100 

 feet a great pocket of oxidized ore was met with, contain- 

 ing the red and black oxides of copper, some carbonates, 

 and some metallic copper and metallic silver ; and it was 

 in this oxidized ore that the new mineral was encoun- 

 tered. It was not at first recognized as a new mineral, 

 and consequently only a few pieces were saved for inves- 

 tigation, the total amount mined probably not exceeding 

 several pounds. 



The mineral has the appearance of an alloy, silver-gray 

 in color with a metallic luster, and slowly tarnishes black ; 

 the streak is lead gray, the hardness 2-5, and the specific 

 gravity 6-14 ; under the microscope it is seen to be homo- 

 geneous. It was found only in a massive form. 



Careful analyses on the purest obtainable samples 

 were made by the writer, at that time assayer and chem- 

 ist for the Mexican Copper Company; these analyses 

 gave the following composition: Copper 6058%, silver 

 27-54%, iron 1-55%, sulphur 9-65% ; the iron is probably 

 an impurity often found as a replacement in copper sul- 

 phide minerals. 



The empirical formula from this analysis is Cu 4 AgS, 

 which corresponds to no known mineral species, though 

 from its similarity to stromeyerite (AgCu) 2 S it might 

 be a variety of that mineral. As an appropriate name 

 for this apparently new mineral, I would suggest Cocin- 

 erite. 



Bureau of Soils, Department of Agriculture, 

 Washington, D. G. 



