Prosopite, Jeffersonite, Covellite, etc. 57 



Fibrous sulphate. 



Mr. W. H. Weed collected in the St. Paul mine, near White- 

 hall, Montana, a magnificent specimen of a compact soluble 

 fibrous sulphate, supposed to be melanterite. It seemed to be 

 a filling between fragments of broken rock. Outwardly it 

 was white from dehydration, but at some depth the unaltered 

 green mineral was to be found. This had the following com- 

 position : 



Al,O s 4-34 



FeO 9-04 



NiO -03 



MnO _ 2-62 



ZnO 1-06 



CuO -05 



CaO -09 



MgO _ 3-07 



Na a O -07? 



S0 3 29-S8 



CI, CO, none 



H 2 48-84 



Insol. *16 



99-25 



Of the water 10 per cent escaped in 24 hours over sulphuric 

 acid and only 4 per cent more in another like period, but a 

 total of 14-4 per cent after 10 days uninterrupted exposure. 

 The water thus lost is very slightly reabsorbed on exposure to 

 air. 



From calculations by Prof. F. W. Clarke the substance may 

 be regarded as a mixture of alunogen or the halotrichite group 

 with salts of the melanterite group, the empirical formula 

 being nearly 



(Fe, Mn) 4 (Zn, Mg),Al,(S0 4 ) 9 . 65H,0. 



The outer white zone of the specimen contained only 39*62 

 per cent of water. 



Laboratory of the U. S. Geological Survey, July. 



