Sp.ar., . 



3-54 





co 2 .... 



16-07 



•365 



CuO.._. 



21-21 



•267 ) 



ZnO— _. 



52-99 



•652 [ 



H 2 0___. 



10-06 



■559 











Theory for 





IT. 



Ratio. 



2RC0 3; 3R(OH) 2 



3-64 









whereCu:Zn=2:5 



16-04 



•365 





1-98 



16-14 



20-00 

 54-36 



•252 ) 

 •669 j" 



•921 



5-00 



20-79 

 53-17 



9-99 



•555 





3-02 



9-90 



108 S. L. Penfield — Chemical Composition of Auriohalcite. 



and 0*64 per cent, of calcite respectively in the two analyses, 

 we have the following with the molecular ratios. 



I. Ratio. 



1-98 



•919 5-00 



3-04 



100-33 100-39 100-00 



The ratios in the two analvses are almost exactly 2:5:3 and 

 the formula is therefore 2EC0 3 , 3E(OH) 2 in which E = Zn 

 and Cu. There seems to be no exact relation between the CuO 

 and the other constituents. In analysis I the CuO : ZnO = 

 about 2 : 5 and using this proportion in the above formula the 

 theoretical composition given above was calculated, which 

 agrees very well with the first analysis. 



The strongest proof of the correctness of the above formula 

 is found in the purity of the analyzed mineral and the exact- 

 ness of the ratio between C0 2 , EO and H 2 0, both of these are 

 as satisfactory as one could desire in mineral analysis, especially 

 for a mineral occurring in minute tufted crystals in a narrow 

 seam with calcite. Moreover the above formula is the same as 

 that proposed by T. Bottger* in the original description of 

 aurichalcite from Loktewsk in the Altai. His analysis was 

 made in Eose's laboratory with great care and evidently on 

 very pure material. 



Other analyses have shown a deviation from the above 

 formula which may have resulted from impurities in the 

 analyzed material or errors of analysis. Thus Delessef has 

 described as buratite specimens from Loktewsk in the Altai 

 and from Ohessy, France, containing as high as 8*62 per cent of 

 CaO, but as A. Belar;}; and others have proved that CaO is not 

 a normal constituent of aurichalcite, it is quite safe to assume 

 that the material Which he analyzed contained calcite ; in fact 

 if CaC0 3 equivalent to the CaO be deducted from his analyses 

 the remainder corresponds closely to the above formula. Other 

 analyses cannot be used in discussing the formula because C0 2 

 and H 2 have not been separately determined ; they are given 

 together simply as loss on ignition. 



A. Belar in a recent contribution on this subject, already 

 noticed, gives four analyses of material carefully selected under 

 the microscope so as to avoid all possible impurities. The 

 analyses are as follows: 



*Pogg. Ann., xlviii, p. 495, 1839. f Ann. Oh. Phys., xviii, 478, 1846. 



\ Loc. cit. 



