114 I '. A. Genth — Contributions to Mineralogy. 



Art. XIII. — Contributions to Mineralogy ', No. 48 ; by 

 F. A. Gekth. 



1. Tetradymite. 



Several years ago, tetradymite was found two miles south of 

 Bradshaw City, Yavapai County, Arizona. It occurs in crys- 

 talline masses, implanted in imperfectly crystallized, slightly 

 ferruginous quartz, associated with pyrite. A few imperfect 

 bladed crystals are visible suggesting an orthorhombic form, 

 combination of the prism and brachypinacoid, with cleavage 

 highly perfect brachydiagonal. Mostly in bladed crystalline 

 masses, the largest blade in my specimens over 30 mm long and 

 6 mm broad. Some of the crystals, partly altered into a brown- 

 ish white, amorphous substance, probably montanite, with a 

 nucleus of tetradymite. After subtracting 15'6 per cent of 

 quartz and 1'8 per cent of ferric oxide, the analysis gave : 



Sulphur 4-50 



Tellurium 33-25 



Bismuth 62-23 



99-98 



This gives nearly : Bi 3 (S 1 Fe^) 3 , analogous to bismuthinite. 



3 . s 

 If the observation of rhombic forms is confirmed, it will place 



tetradymite (with exception perhaps of that from Schubkan), 



in its proper place in the system, in the grouj) with stibnite 



and bismuthinite. The quantity of the altered mineral was 



too small for a fuller examination. 



2. Pyrite. 



The occurrence of arsenate of cobalt with the octahedral 

 crystals of pyrite at the French Creek, Chester Co., Pa., Iron 

 Mines, suggested the examination of the latter which was 

 made in my laboratory by Mr. Aron Hamburger. The most 

 perfect and purest crystals, averaging about 2 mm in size, gave 

 the following composition : 



S 54-08 



As.. 0-20 



Cu 0-05 



Ni 0-18 



Co 1-75 



Fe 44-24 



100-50 



