1887.1 "^l [Qenth. 



cimens of this rare species, which have furnished the material for the fol- 

 lowing investigation : 



It occurs at the San Antonio mine in the mineral district of San Rafael, 

 Sierra de Tapalpa, Sayula Canton, Stale of Jalisco, Mexico. 



It has a finely granular structure and a pale steel-gray color, inclining 

 to lead-gray. Lustre dull metallic; soft. 



Associated with pyrite, galenile, quartz and a silicate of aluminum and 

 calcium, and so much intermixed with them that it was impossible to ob- 

 tain pure material for analysis. The puiest that could be selected was 

 free from pyrile, but contained about 7 to 8 per cent of galenile and the 

 same quantity of quartz and silicate. The specific gravity, which was 

 found to be = 6 739, was approximately calculated for the pure mineral, 

 and gave — 7.744. 



Portions from two pieces, A and B, apparently equally pure, were 

 analyzed. A by dissolving in nitric acid; B by fusion with sodium 

 carbonate and sulphur — the sulphur in B was determined by fusion with 

 sodiuni carbonate and nitrate, lixivialion with water and five times re- 

 peated evaporation with hydrochloric acid in order to reduce the telluri- 

 to tel!urous#acid and precipitation of the sulphuric acid by barium chloride. 

 The tellurium was always weighed as tellurous oxide. 



= 3 



= 1 



= 1.15 



= 1.85 



= Ag, Bi (STe)3 or 3 Ag, (STe). Bi, (STe)3 



The above average analysis and the atomic ratio of the constituents 

 found give the following percentages : 



— 6 Ag = 648 = 43.76 



— 2 Bi = 420 = 28.36 



— 2.3 Te = 294.4 = 19.88 



— 3.7 S = 118.4 = 8.00 



100.00 1480.8 100.00 



PROC. AMEK. PHILOS. 80C. XXIY. 125. P. PRINTED APRIL 28, 1887. 



