Decomposition of Iron Pyrites. ; !< s "> 



land, Thuringia, Hungary, Piedmont, Scotland, Cornwall, Bra- 

 zil, Africa, etc. : 



Octahedra, at Schmalkalden : 



Pentagonal dodecahedra, in Bohemia, Rhenish Bavaria, and 

 Scotland. 



Hematite and specular iron after pyrite: 



At Ouval, Bohemia; at Hoy, in the Orkneys; at Kerrara, 

 Scotland, etc. : 



Cubes, at Triblic and Posedlitz, etc. : 



Octahedra, at Frassem, near Arlon : 



Peutagonal dodecahedra, at Lindenberg : 



Pyritohedrn, in Eio, Elba. 



Magnetite, in little cubes after pyrite, near East Tarbet in Argyle- 

 shire, and near Portrush, Scotland, 4 " etc. 



However, the pseudomorpbs in the crystalline iron oxides, 

 both specular iron and magnetite, after pyrite, may owe their 

 origin to more complicated processes of alteration, besides those 

 concerned in mere decomposition by weathering. 



Sulphur also is separated, in association with the hydrated 

 iron-oxide, in many cases of the decomposition of pyrite (as at 

 Bodenmais, Bavaria; at Frassem, near Arlon; at Burnt Hic- 

 kory, Georgia, etc.), and also, in association with copperas, in 

 that of marcasite (as at Schriesheim). Dr. J. S. Newberry 

 states his observation of considerable quantities of free sulphur 

 on the waste dumps of pyritiferous shales from the coal mines 

 of Ohio. G. Rose observed at Beresowsk, Siberia, that the 

 cubical cavities, left in the rock after the complete decomposi- 

 tion and removal of the pyrite crystals, still retained minute 

 glittering crystals of sulphur. 41 As Senft remarks, "it has 

 been proposed to explain this kind of decomposition by means 

 of aqueous vapors" ("perhaps at elevated temperature," Blum), 

 " which are decomposed by their reaction with the iron pyrites, 

 and, by means of their oxygen, have altered the iron into hy- 

 drated oxide, while simultaneously their hydrogen has united 



40 Roth, op. cit., I, 235, 236. 



11 Reise nack dem Ural, I, 196 and 214. 



