368 Decomposition of Iron Pyrites. 



4.494. Two other compounds have been prepared by Arfvedson, 

 to which he assigned the formulas, Fe 8 S and Fe 2 S. 



Of these iron sulphides, there are probably but two of whose 

 occurrence in nature we have any certain knowledge, viz., the 

 Proto- and Disulphide. 



Iron protosulphide, Fe S, containing in 100 parts : iron, 63.64, 

 and sulphur, 36.36. 



This substance has not been recognized as an individual 

 mineral on our globe, except in the form of the foreign mineral 

 troilite, which occurs in many fallen aerolites. 



The nature of this interesting mineral has been shown by 

 many analyses, of which it will suffice to present one by J. Law- 

 rence Smith, on troilite derived from the aerolite which fell in 

 Sevier County, Tenn. : iron, 63.80, and sulphur, 36.28. 



The specific gravity of the mineral varies in different stones 

 from 4.681 to 4.817. 



As this mineral has separated from fusion, and owes its origin 

 to extra-terrestrial agencies and conditions of which we are en- 

 tirely ignorant, it cannot be safely used for discussion in relation 

 to the density of the iron sulphides of our own planet. 



In the black mud of ditches, pools and salt-marshes, of flats 

 at low tide, and that between the stones of city pavements, in 

 peat, and in trunks of trees lying submerged along the sea- 

 beaches, the presence of an amorphous iron protosulphide has 

 been verified, in black particles, without metallic lustre, readily 

 decomposable by hydrochloric acid, 9 or even by exposure to the 

 air, with an efflorescence of copperas. 



The sulphide occurs, also, in combination with nickel sul- 

 phide, in the form of a single bronze-colored mineral, pentlandite, 

 an ore of nickel, first found at Lillehammer, Norway, and whose 

 composition, according to Rammelsberg, 10 is as follows: iron, 

 40.60; sulphur, 36.64; nickel, 21.07 ; and copper, 1.78. Spe- 

 cific gravity, 4.6. 



Separating the intermixed chalcopyrite (5.14 per cent.) repre- 

 sented in this analysis, the mineral is found to consist of iron 

 sulphide (Fe S), 64.73, and nickel sulphide (Ni S), 34.45. 



9 A. Daubree, Etudes Syn. de Geol. Exper., (1879), 87. 



10 Fogg. Ann. (1864), CXXI, 337. 



