204 



University of California. 



I Vol,. 3. 



any coating' of pyrite. It is very brittle and shows a good basal 

 cleavage. The crystals, which have lain in trays, exposed to 

 the air for almost a year, have not become ocherous externally. 

 Exposed to the sunlight, however, they become white and opaque. 



Cold water readily dissolves the crystals, from which solution 

 ferric hydrate is copiously precipitated on heating. Its pyrog- 

 nostic characters are similar to those of melanterite, except that 

 it readily gives a reaction for copper. Heated in a closed tube, 

 it readily melts in its water of crystallization and on stronger 

 ignition is reduced to a black, magnetic mass. Its hardness is 

 about 2.5 and its specific gravity is close to 1.8-1.9. 



Chemical Properties . — It was not possible to pick out enough 

 material for an analysis, without including a good deal of pyrite. 

 The abundance of the mineral, however, allowed of several 

 analyses of different specimens, the average of which analyses is 



seen in the table 



s below. 











Average 



Same with 



Molecular 



Calculated 





Analysis. 



Insol. deducted. 



Ratio. 





CuO 



13.39 



15.73 



1.11 



14.11 



FeO 



10.48 



12.31 



.97 



12.75 



no. 



24.02 



28.21 



2.00 



28.40 



H 2 



38.44 



45.14 



14.23 



44.74 



Insol . 



14.85 











101.18 



1(11.39 





11)11.00 



The last column is the calculated percentage for the formula 

 CuO. FeO. 2SO.s +14 H 2 0. 



Water was given off at the temperatures stated in the follow- 

 ing proportions : 



Ratio. 



HoO(110°) 33.58 6.11 



H 2 (above 200°) 4.86 .89 



Practically no water is given off between 110° and 200°. It 

 would thus seem as if f of the water content of pisanite is given 

 off at a low temperature and that nearly twice that temperature 

 is necessary to expel the last molecule of water, a fact which 

 suggests that, structurally, the six molecules play a different 

 role from the seventh. The six molecules are water of crystalli- 

 zation while the seventh is constitutional water. 



