Genth and Penfield — Contributions to Mineralogy. 383 



tion of any cavernous crystals I thought they might show a 

 different composition. 



The analysis gave : Calculated : 



Ag 84-40 Ag 85*06 per cent. 



Cu 0-49 S 11-03 " 



S 11-36 Se 3-91 " 



Se (by diff.) 3-75 



100-00 



100-00 



This is the composition of argentite in which -§- of the 

 sulphur is replaced by selenium. The composition correspond- 

 ing to : -§Ag 2 Se-l |Ag 3 S is given above. 



e.- A specimen of acanthite from Guanajuato, Mexico, pre- 

 sented to me by Messrs. Geo. L. English & Co., was analyzed 

 for the purpose of seeing whether it contained selenium, but 

 was found to be entirely free from it. 



Elongated, wirelike distorted crystalline particles in calcite. 

 The analysis gave a trace of quartz and calcite and — 



As? 86-79 



S". .- 13-20 



99-99 



2. Metacinnabarite. 



To Professor Gustav Guttenberg of the Central High School 

 at Pittsburg, I am indebted for an interesting occurrence of 

 metacinnabarite in irregular particles of from 5 to 10 mm in 

 diameter, disseminated through a ferruginous, laminated barite, 

 from San Joaquin, Orange County, California, where it had 

 been collected by one of his pupils. 



Color iron-black, but many pieces show already a partial 

 change into ordinary cinnabarite, both by a good lens and the 

 reddish black powder which some of .,the particles yield on 

 pulverizing. Fracture conchoidal, brittle, soft. Sp. gr. 7'706. 

 The analysis gave : 



Hg 85-89 



S 13-69 



CI 0-32 



99-90 



It is remarkable that all the fragments which were examined 

 showed the presence of chlorine. The 032 per cent of CI 

 which were found would indicate an admixture of 1'23 per 

 cent of calomel. 



Am. Jour. Sci. — Third Series, Vol. XLIV, No. 263. — November, 1892. 

 26 



