66 E. V. Shannon — Mullanite, a new Member of the 



Art. V. — On Mullanite, a new Member of the Jame- 

 sonite Group, from Two Localities; by Earl V. 

 Shannon. 



Quite recently the present writer published a short 

 note on the occurrence of the rare sulphantimonite, epi- 

 boulangerite, at the Iron Mountain mine, near the town 

 of Superior, in western Montana. 1 Very soon after this 

 note was submitted for publication, there was obtained 

 a mineral very similar in appearance and associations, 

 from the Gold Hunter Mine, near the town of Mullan, in 

 the Coeur d'Alene District, Idaho. Only a small amount 

 of the Idaho material was available and the most strik- 

 ing fact brought out by the preliminary investigation 

 was that the streak was distinctly brown, while that of 

 epiboulangerite is dull grayish black. A request for 

 more of the mineral was directed to the Gold Hunter 

 Company, and Mr. C. L. Herrick, manager of the mine, 

 responded by sending some excellent specimens. While 

 awaiting the arrival of the Idaho material, the writer 

 undertook to analyze more completely, a very fine speci- 

 men of the sulphantimonite from the Iron Mountain 

 mine. The streak of this mineral was found to be brown 

 like that of the Gold Hunter material, and analysis 

 showed that it was not epiboulangerite but a mineral hav- 

 ing the composition expressed by the formula 5PbS.- 

 2Sb 2 S 3 . The mineral from the Gold Hunter Mine, later 

 received from Mr. Herrick, proved to have the same 

 composition. 



While the composition is essentially that of a silver- 

 free diaphorite, that mineral as described contains silver 

 to the amount of around 23%, the ratio of Pb: Ag 2 being 

 4 : 3. That the compound is distinct, and not a variable 

 mixture of the two end members, 5PbS.2Sb 2 S :i , and 

 5Ag 2 S.2Sb 2 S 3 , is established by the fact that the com- 

 pound 5(Pb,Ag 2 )S.2Sb 2 S :j in its two forms, has been 

 found from a number of widely separated localities, yet 

 in all observed occurrences the silver and lead are pres- 

 ent in the same ratio. The mineral described below can 

 thus no more be regarded as a variety of the species 

 diaphorite than chalcocite can be regarded as a vari- 

 ety of stromeyerite, or than calcite can be regarded as 

 a variety of dolomite. The mineral here described is 

 free from silver and hence seems to deserve a distinctive 



1 American Mineralogist, vol. 2, No. 11, 1917. 



