Brown.] ^^^ [May 18, 



Marcasite, on the other hand, has a pale greenisli or grayish yellow 

 color, aa uneven Iraclure, which shows a somewhat fibrous structure, 

 and generally but little lustre on the surface of fracture. It crystallizes 

 in the orthorhombic system, very commonly in twins or radiated fibrous 

 masses. It is not very permanent in moist air, but readily decomposes 

 and largely into FeSO^. The chemical formula of either form, calculated 

 from quantitative analyses, is the same, FeSj or Fe = 40.67%, 8^=53.33%. 



The chemical study of these two minerals has been mainly confined to 

 the formation of one of them artificially and to a few experiments on 

 their relative decomposability. Pyrite has been made artificially in a 

 number of ways ; marcisite has not as yet been formed ariificially.* In 

 1836, Wohlerf produced cubes and octahedra of pyrite by subjecting a 

 mixture of ferric oxide, flowers of sulphur and ammonium chloride to a 

 temperature a little above the volatilizmg point of the ammonium chlo- 

 ride. The resulting mass was washed to isolate the crystals Irom the 

 accompanying pulverulent matter. Stanislas Meunier J modified this 

 method by mixing equal parts of ferrous carbonate and sulphur and heat- 

 ing in glass tubes over a moderate flame. When the excess of sulphur 

 has been driven otf, there remains a black powder containing a consider- 

 able percentage of cubes of pyrite. Dana § states that pyrite may be 

 made " by slow reduction of ferrous sulphate in presence of some carbon- 

 ate." Baubigny 1| produced FelSj as a crystalline crust by acting on 

 metallic iron by a solution of SO^ in water (Hj'^Og) in closed tubes and 

 at a temperature of 200-. As neither this experiment nor the one imme- 

 diately preceding it shows that the crystals were isometric, it is possible 

 that both of them may be marcasite. Henri Saint Claire DevilleT[ pro- 

 duced cubes of pyrite by melting a mixture of potassium sulphide (KjS) 

 and iron sulphide (FeS) in presence of excess of sulphur. This reaction, 

 if correct as to the cubical product, is a remarkable one, as I should rather 

 expect marcasite to result under such conditions. Senarmont** produced 

 FeSj by decomposing a salt of iron by an alkaline sulphide at an elevated 

 temperature in sealed glass tubes. The product was an amorphous black 

 powder, not altering on exposure to air and not attacked by hydrochloric 

 acid. This may have been pyrite, as marcasite is readily decomposed by 

 moist air. Rammelsberg.f-j- in 1863, made FeSj pseudomorphs after ferric 

 oxide (FcjOa) by passing a current of hydrogen sulphide over it at a tem- 

 perature between 100- and a red heat. The product of this reaction would 

 likely be pyrite. 



In nature ii would seem that in most cases the sulphide of iron first 



*I)oelter, Zeit.fiir KrysL, xi, 31, 18S5 ; cf. Dana, Sijsl. Mlii., 1892. 



t Pog<j. Ann., xxxvii, p. 238. 



X Lcs Melhodcs de Synthfxc en Mineralogie, S. Meunier, 1891. 



§ J. U. Daua, System of Mineralogy, edition of 1808, p. 61. 



II S. Meunier, Synth. Min., p. 279. 



1l Cited in Vict. Ckem. of U'Hriz, by E. Wilm, article " Iron," T. i, p. 1111. 



**S. Meunier, Synth. Min., p. 2S5. 



tt </o«r. Jilr Praktische Clicmic, T. Ixxxviii, p. 2C6. 



