604 Ford and Bradley — Hetcerolite from Leadville. 



" probably contained in a slight admixture of chalcophanite." 

 To the present writers it does not seem as if the water at 

 least could be so easily eliminated from the analysis. At any 

 rate the explanation of the probable cause of its presence 

 seems to be untenable. Chalcophanite contains, theoretically, 

 12'5 per cent of water. Consequently, if the 3*89 per cent of 

 water given in the above analysis was due to admixture of 

 chalcophanite, nearly one-third of the material analyzed must 

 have been that mineral. Further, over 9 per cent of manga- 

 nese dioxide derived from that amount of chalcophanite would 

 also have been present. If the water found is included in the 

 analysis, the following composition and ratios are derived : 



ZnO 3393 0-416 2*00 



Mn 2 3 ._.. 61-24 0-388) 



Fe 2 3 0-78 0-004 \ ° 392 l 88 



H 2 3-95 0-220 1-05 



100-00 



The formula derived from the above calculation is the same 

 as that derived from the analysis of the Leadville mineral. 

 Whatever the correct interpretation of the analyses may be, it 

 is certain that the specimens from the two localities are to be 

 considered the same chemically. Prof. Palache kindly sent to 

 us a specimen of the Stirling Hill material for comparison, and 

 it agrees perfectly with the Leadville mineral in all physical 

 and optical tests. It may be that the exact composition of 

 hetaerolite cannot be definitely settled until purer material can 

 be analyzed. With the evidence at hand, however, the present 

 writers prefer to include the water as an essential part of the 

 composition, making the formula 2Zn0.2Mn 2 3 .lH 2 0. 



Mineralogical Laboratory of the Sheffield Scientific School 

 of Yale University, New Haven, Conn., 

 March 11, 1913. 



