402 Decomposition of Iron Pyrites. 



indeed always more or less represented in any locality in which 

 these minerals abound. Some of the first distinct observations 

 of this fact were thus recorded by Stromeyer, in the study of 

 certain pyrrhotite ores : 



" The magnetic pyrites of Fichtelberg and Breitenbrunn were 

 so intimately intermixed with pyrite that it was impossible to 

 separate it from them." 78 



He also observed a similar intimate intergrowlh at other local- 

 ities, in the following per-centage proportions: 



Pyrrhotite. Pyrite. 



Treseburg, Hartz Mts., - - 96.08 3.02 



Bareges, Upper Pyrenees, - - 75.58 24.42 



Since the proportion of the pyrite in these magnetic pyrites 

 was found very constant, and the fragments employed for analy- 

 sis had been previously purified from all visibly intermixed pyrite 

 with the utmost care, with the assistance of a magnifying glass, 

 Stromeyer considered it very probable that this pyrite was not 

 mechanically intermixed with the magnetic pyrites, but occurred 

 chemically dissolved in it, and that the considerable quantity of 

 the same in the magnetic pyrite of the Pyrenees accounted for 

 its feeble magnetism. 



This view, however, was at once controverted by Berzelius, 79 

 who found that on slicing and polishing the same magnetic py- 

 rites, the intermixed pyrite was seen crossing it. with different 

 color and hardness, and was therefore not dissolved in it. 



A similarly intermixed growth of these two minerals, or the 

 enclosure of crystals of one within the other, has been observed 

 by G.Rose. 80 



Kenngott 81 later called attention to a like intergrowth in a 

 specimen of pyrite, associated with marcasite, from Tavistock, 

 Devonshire. In this it was evident that these dimorphous spe- 

 cies had crystallized simultaneously ; both were well intermixed, 

 and even intergrown in the same crystal, plates of one often in- 

 tersected the crystals of the other, and minute or drusy crystals 



78 Gilb. Ann. (1814), XL VIII, 186 and 163. 



79 Gilb. Ann. (1814), XL VIII, 209. 



80 Reise nach dem Ural, II, 117 ; Pogg. Ann. (1849), LXXIV, 293. 



fel Sitzungsb. k. Akad. Wiss. in Wien (1853), X, 293 (Min. Notiz., No. 2). 



