370 Decomposition of Iron Pyrites. 



It is not easy to make a comparison of actual analyses of pure 

 crystals of these minerals with the densities obtained, as most 

 of the analyses have been made upon massive forms for com- 

 mercial purposes. From the scattered literature of the subject 

 the following tables have been compiled. The full details of 

 chemical composition and density are the more required for 

 our purpose in that they are but meagerly presented in all the 

 treatises on mineralogy — the analyses of pyrite being generally 

 entirely omitted. 



Pykrhotite. 



Synonyms — Magnetkies (Hausmann), pyrite magnetique, mag- 

 netic pyrites, pyrrhotine (Haidinger), rhomboedrischer eisenkies 

 (Mohs). 



The results of all the chemical examinations of this mineral 

 by various analysts, have been very fully presented by H. Haber- 

 mehl, in his excellent paper, 11 and need not be repeated here. 



These analyses yield formulas which vary widely, thus : — 

 Fe 5 S 6 , Fe 6 S 7 , etc., up to Fe 16 S 17 , the mineral apparently con- 

 sisting of some form of combination of molecules of Fe S with 

 a vayring number of Fe S a ; or, according to another view, of 

 Fe S with Fe 2 S 3 . To determine whether this form of combi- 

 nation be a true chemical compound, an isomorphous mixture of 

 sulphides, or a mere mechanical mixture of Fe S with Fe S 2 , 

 F 2 S 3 , or S, has been the object of much investigation. The 

 analyses by Habermehl of fifteen samples, successively sepa- 

 rated, by the magnet from the pulverized mineral of Bodenmais, 

 show, by their accordant results, that the last theory, that of 

 mechanical mixture, may be put aside as impossible. 



The fact that, on solution of most varieties of pyrrhotite in 

 hydrochloric acid, only sulphur is left behind, although Fe S 2 is 

 in every other form insoluble, has been considered an objection 

 to the supposition of the presence of iron disulphide. Its minute 

 molecular subdivision may perhaps account for its solubility in 

 this instance, but the question still remains unsettled. 



In the following table are presented all the published deter- 



11 Ber. d. oberhess. Ges. f. Natur. u. Heilk. (1879), XVIII, 83, and 

 Jahrb. f. Min. (1880), II, 303. 



