Decomposition of Iron Pyrites. 393 



But the observations of Breithanpt and BischorT" point de- 

 cidedly to quite another solvent, method of reaction, and signifi- 

 cant product. 



According to Breithanpt 6 '"': "it is not improbable that many 

 iron-pyrites of the Freiberg lodes were once pyrrhotite. Pyrite 

 is also always the more recent product, even where it occurs in 

 association with pyrrhotite. . . Marcasite occurs also in hex- 

 agonal prisms, pseudomorphous after pyrrhotite, in part often 

 and regularly intermixed with pyrite. . . The pseudomorphs af- 

 ter pyrrhotite exhibit almost throughout acontraction of volume/' 

 indicated by abundant cavities which are occupied by crystals of 

 pyrite, quartz, and other minerals. In Wunsiedel, the pyrr- 

 hotite was observed to pass into pyrite with a diminution of bulk. 

 Both 66 remarks that " in the alteration of pyrrhotite into pyrite, 

 a part of the iron is removed. Breithaupt observed that on the 

 larger pseudomorphs of the kind in Freiberg, carbonate of iron 

 occurred, partly with other carbonates containing iron-protoxide. 

 Calcite and quartz are other abundant associates." 



Bischoff states : 



" The lodes near Freiberg not infrequently contain pseudo- 

 morphs of iron pyrites after magnetic pyrites, though the latter 

 mineral occurs but very rarely. Wherever the two minerals are 

 associated, the iron pyrites is always the more recent of the two ; 

 and probably much of the iron pyrites in lodes was originally 

 magnetic pyrites. 



••In the conversion of magnetic pyrites into iron pyrites a por- 

 tion of the iron would be removed ; and, consistently with this, 

 it appeal's that in the neighborhood of Freiberg, where this 

 alteration has taken place very extensively, the magnetic pyrites 

 has furnished material for the production of iron-spar and other 

 minerals containing protoxide of iron. Therefore the iron has 

 been extracted from magnetic pyrites by the action of carbonated 

 water. In this alteration the magnetic pyrites must lose 25.54 

 per cent, of iron ; and, since the density of iron pyrites is greater 

 than that of magnetic pyrites, the volume of the former would 



" Cbem. and Phys. Geol. (1859), III, 455-456. 

 ,;:> Pangenesis, pp. 130, 161-164 170. 

 ,;,; Op. cit., I, 242. 



