214 



University of California. 



[Vol.. 3. 



Analysis. 



Ratio. 



CuO 31.14 



FeO none 



MgO trace 



SO, 32.06 



H.O (110°) 28.20 

 H 2 (above 110°) 7.50 



Insol. .81 



1.00 

 3.91 

 1.04 



.97 



4.95 



99.71 



Considering, as before, that the water given off at 110° is 

 water of crystallization, while the remaining molecule is consti- 

 tutional water, we may write the formula of chalcanthite, 



This formula differs from that of boothite only in the fact that 

 it has four molecules of water of crystallization, instead of six. 



General Description. — A yellow ferric sulphate is quite abun- 

 dant, both at the mine and in the immediate neighborhood, 

 which agrees well in its various properties with copiapite. Some 

 distance from the mine, on what is probably an old prospecting 

 dump, a thick layer of copiapite occurs which was selected for 

 the analyses. Some distinct, though microscopic ciystals, 

 occur associated with pisanite, but the entire amount of this 

 material is too small for a chemical analysis. 



Under the microscope, with the highest power, the minute 

 crystals are seen to be six-sided tabular crystals, nearly colorless 

 and nonpleochroic if thin, but somewhat pleochroic if rather 

 thick. The pleochroism is colorless to pale yellow. Cleavage is 

 perfect parallel to the plates, which are probably copiapite crystals 

 tabular to the clinopinacoid. They are too small to show the 

 emergence of a bisectrix. 



Chemical Properties. — Under the microscope the material 

 analysed was seen to consist of a granular mass with no distinct 

 crystals, with which a few colorless prisms were intermixed. 

 Some of these prisms give parallel extinction and are probably 

 epsomite while others give varying angles of extinction up to 



CiiS0 4 .H 2 0+4H 2 0, or structurally, OS 



+4H,0. 



COPIAPITE. 



