F. R. Van Horn — Pisanite and Arsenopyrite. 43 



of magnesium in small quantities. In analysis 3 by Schaller 

 much more magnesia is found than in the Isabella mineral. 

 In order to calculate the formula from the analysis, since the 

 magnesia replaces ferrous iron, it has been recalculated as that 

 substance with the following results : 





Kecal culated 



Combining 



Molecular 





analysis 



weights 



ratio 



S0 3 



27-87 



•348 



3-25 



(FeO,MgO) .. 



18-02 



•251 



2-34 



CuO... 



8-50 



•107 



1-00 



HO 



46-47 



2-585 



24-15 



100-86 



The molecular ratios obtained from analysis 2 by Schaller 

 are 2FeO.Cu0.3S0 3 + 21IIO, and the ratios of the blue pisanite 

 from Isabella conform very closely to this formula, with the 

 exception of the water, which is 3 molecules too high and must 

 be ascribed to moisture in the original substance. The theo- 

 retical percentage required by the formula 2FeO.Cu0.3S0 3 4- 

 21H 2 would be as follows : 



S0 3 . 28-53 



FeO 17-08 



CuO 945 



HO 4494 



100-00 



Green Pisanite. — The results of the analysis of the green 

 mineral were obtained by Dr. Yeazey as follows : 



S0 3 28-72 



FeO 21-45 



CuO 3-83 



MgO .. 0-39 



HO 45-58 



99-97 



When this analysis is compared with that of the blue vari- 

 ety, the most noticeable differences are the increase of iron 

 and decrease of copper which was to be expected from the 

 green color. In other words, the green mineral is a pisanite 

 nearer melanterite, whereas the blue substance is a pisanite 

 approaching the rare mineral boothite (CuS0 4 + 7H„0), which 



