374 Decomposition of Iron Pyrites. 



According to Senft, 11 it decomposes slowly, but, according to 

 Roth, 14 more easily than pyrite, into copperas and reddish brown 

 iron-oxide. Copperas was observed on pyrrhotite, near Boden- 

 mais ; sulphate of iron and nickel on nickeliferous pyrrhotite, 

 at Horbach ; limonite, pseudomorphous after pyrrhotite, near 

 Ehrenfriedersdorf ; and gothite after pyrrhotite, at Wal den- 

 stein, Carinthia. These indicate the hepatic mode of alteration. 

 G. W. Hawes 15 stated, that, in ]STew Hampshire : — 



"The magnetic pyrites do not decompose so readily as ordi- 

 nary pyrites. I have seen some gneiss from our State in build- 

 ings, and though the stone was sprinkled with particles of mag- 

 netic pyrites, it had not become stained by long exposure to the 

 weather." 



Prof. C. H. Hitchcock 16 corroborated this view : — 



"One thing should be said of this impurity in the Hanover 

 rock. There is a building on Corey Hill, containing pieces of 

 the pyrrhotite as large as beechnuts ; and, though the house has 

 been standing nearly seventy years, there are scarcely any iron 

 stains upon it. This species of pyrites sustains itself so well 

 that oftentimes its presence need not be feared. A more re- 

 markable instance of the ability of this pyrites to resist decom- 

 position may be seen in the Francestown soapstone. I have 

 examined many of the stoves manufactured from this stone, 

 and noticed that bright particles of this pyrites were thickly 

 sprinkled through it. I have also looked at pieces of this stea- 

 tite that had been subjected to great heat without much change. 

 It would appear, therefore, that this mineral may not be in- 

 jurious to granites, as it seems to withstand successfully the 

 vicissitudes of both heat and cold." 



On the other hand, D. Forbes 17 stated, in regard to the pyrr- 

 hotite ore of Inverary, Scotland : — 



"After some time, on exposure to the air, the mineral crum- 

 bles to pieces, some specimens breaking up after a few months, 

 whilst others have resisted as many years." 



13 Lehrb. d. Min. u. Fels. (1869), 176. 



14 Allg. u. chem. Geol. (18T9), I, 103. 



15 Geol. of New Hampshire (1878), Pt. IV, 31. 



16 The Geol. of New Hampshire (1878), Pt. V, 80. 



17 Phil. Mag. (1868), 4th Series, XXXV, 179. 



