SCHALLKR.] 



Minerals from Leona Heights. 



205 



As with melanterite, the formula for pisanite may be written, 



OS +6H..O 

 \ g>H 2 



where R represents (Fe,Cu) in the ratio of 1:1. Pisanite may 

 then be regarded as a salt of tetrahydroxyl sulphuric acid, 

 OS (011)4, in which half of the hydrogen is replaced by iron and 

 copper in equal proportions. 



Just what the temperature is, at which all of the six mole- 

 cules of water of crystallization are driven off, is difficult to say. 

 It is probably not far from 100°-110°. A temperature of about 

 250° will probably expel all of the water of the mineral. 



A partial analysis of a specimen of pisanite, with a larger 

 amount of insoluble matter, gave: 







Ratio. 



CuO 



8.60 



.99 



FeO 



7.61 



.97 



SO;, 



17.53 



2.00 



We thus have good evidence that the pure crystals of pisanite 

 have the definite formula FeO.Cu0.2SO :! .2H 2 + 12 H 2 0. 



The original analysis of pisanite, by Pisani,* gives a ratio 

 agreeing quite well with this formula. His analysis, together 

 with the ratios calculated therefrom, is: 



Ratio. 



CuO 15.56 1.04 



FeO 10.98 .82 



SO :! 29.90 2.00 



H>0 4li.56 (by dift'.'O 12.95 



100.00 



Analyses of other specimens show that this ratio is not 

 necessarily constant. The material is much poorer and is not in 

 good crystals, like the pisanite already described. An analysis 

 of the specimen collected by Mr. Booth is given in the table 

 below. In the last column is given the composition calculated 

 from the formula 2FeO.CuO. 3S0 3 +21 H 2 0. 



*Comptes Rendus, 1859, 48, 807 



