382 



Decomposition of Iron Pyrites. 



Pyrite. 



Fe. 



Earthy 

 8. impu- S. G. 

 rities. 



L'AJlier, 



44.2 



52.7 



3.1 



4.803 



At Isserpent. 



Elba, - -' - 



43.5 



52.2 



4.3 



4.801 



In the specular ores. 



Confleas, 



43.1 



52.4 



4.5 



4.810 



Ariege. 



L'Aude, - 



43.5 



49.1 



7.2 



4.743 



Carcassonne. 



Lavoulte, 



42.9 



48.7 



8.2 



4.771 





Allevard, - 



42 1 



48.5 



8.9 



4.750 



Isere. 



Gard, - 



40.5 



48.5 



10-7 



4.732 





Chessy and Sain-Bel, 



39.3 



46.5 



14.0 



4.621 





Marcasite. 













Beauregard, etc., 



44.0 



50.7 



5.0 



4.207 



From ammonites. 



Creusot, 



32.5 



49,1 



8.0 



4.181 



From coal-beds. 



St. Etienne, 



42.3 



48.5 



8.6 



4.180 



From coal-beds. 



Ain, 



42.0 



48.2 



9.6 



4.182 



From Oolite ore-beds. 



Champagne, 



40.9 



46.4 



12.2 



4.176 



Nodules. 



Oise and Aisne, - 



38.9 



44.9 



15.7 



4.177 



Bituminous pyrites. 



It is thus well shown in each of these minerals, that, with 

 the increase in the percentage of earthy impurities, e. g., silica, 

 alumina, lime, organic matter and water (passing down the 

 fourth column), a corresponding decrease is generally shown in 

 the specific gravity figures (passing down the fifth column). 



Kenngott and v. Zepharovich found in their examination of 

 pyrite-crystals, that, in those which were perfectly fresh and 

 bright, the specific gravity lay between 5.0 and 5.185, but that, 

 in the others, "'through the intimate intermixture with quartz, 

 or by incipient decomposition, it sank down to 4.8 and 4.7." 



The influence of the partial substitution of isomorphous sul- 

 phide combinations of copper, nickel, etc., is presented in many 

 analyses of pyrrhotite, and in Xos. 16 (balanced by the en- 

 closure of light gangue) and 17 of pyrite. 



Weathering of Pyrite. 



On the exposure of this mineral to weathering, both of the 

 main constituents, iron and sulphur, may combine with the 

 oxygen of the air at the ordinary temperatures, in the presence 

 of moisture, producing iron oxide, iron sulphates (copperas, etc.), 

 sulphur, and even free sulphuric acid. When this action occurs 



