216 



University of California. 



LVOL. 3. 



that 24.2 per cent, of water be given off at the first temperature, 

 about 110? Structurally, the formula for copiapite would then 



become, 



OS 



OS 



o 

 o 







o 



°>H, 

 8>H, 



Pe 



H _ 



+14H 2 0. 



EPSOMITE. 



General Description. — Epsomite occurs in the mine, and was 

 also frequently observed in the immediate vicinity, as an efflores- 

 cence. It occurs as bent and curved fibrous prisms, showing, 

 however, no crystal surfaces. Under the microscope the prisms 

 give straight extinction. 



Chemical Properties. — The analysis served merely to identify 

 the mineral. 



Calculated. 



16.3 

 32.5 



51.2 





Analysis. 



Insol. deducted. 



MgO 



12.4 



14.8 



so 3 



26.5 



31.7 



H,0 (110°) 



34.1 



40.8 



H.O (above 110°) 



10.2 



12.2 



Insol. 



16.3 





A1,0, 



trace 



trace 



FeO \ 







CuO J 



none 







99.5 



99.5 



100.0 



The formula for epsomite may be written, like that of 



/ O- 



melanterite, OS 



>Mg 

 >H 2 



+GEUO. 



ALUNOGKN. 



A coating of white powder, intimately associated with 

 pieces of copper sulphate, covers the bunkers in front of 

 the mine. The powder is readily soluble in cold water, 

 which solution gave tests for copper from the admixed copper 

 sulphate, aluminum, sulphuric acid and water, with traces of 

 ferrous iron and magnesia. Under the microscope the mass 

 consists of a granular aggregate of a white mineral, only 

 partially transparent. The mineral agrees, so far as can be 



