210 Decomposition of Iron Pyrites. 



1. Density of Normal Pyrite. In considering the variations 

 of density shown in the third column of the preceding table, the 

 higher numbers, near the head of the column, are open to serions 

 suspicion, from the probable intermixture of galenite, gold or 

 other heavy impurities. The still higher figures 5.158-5.185, 

 obtained by Breithaupt, Kenngott/ and Zepharovich, are put 

 asid(5 by Rammelsberg,^ as too high and he accepts the figure 5.0 

 as representing the true specific gravity of the pure mineral. 

 The general tendency of the enclosed impurities, marcasite, 

 chalcopyrite, sphalerite, quartz, etc., has been to lower the spec- 

 ific gravity figuies, and for this reason we may reject the ten at 

 the bottom of the series. We thus come to the conclusion that 

 the specific gravity of pure normal pyrite must approximate 

 closely to the figure 5.01, which includes the typical and perfect- 

 ly stable varieties from Colorado, Arizona, Waldenstein and 

 Chili, (Nos. 5, 9, 13, 15, 16, and 17). However, wide variations 

 of density, color, and therefore of constitution, in the crystals of 

 the same locality, appear at many points in the foregoing series. 

 Some prominent instances have been already given to illus- 

 trate this local variation, in the Table for the density of Pyrite, 

 in Parti, of this paper; entire reliance cannot be placed in 

 those results, unfortunately, from the method, commonly em- 

 ployed, of determining the specific gravity on whole crystals. 

 The fact of great local variation in density, however, is confirmed 

 by my own figures, a few of which may be tabulated below, 

 with those by other observers from the same localities marked 

 by an asterisk. 



Locality. 



Specific Gravity. 



Traversella, Italy. 



5.097* 



5.078* 



5.016* 



4.985 



4.967* 



Freiberg, Sax. 



5.031* 



5 007* 



5.001* 



4.916 



4.619 



Elba. 



5.027* 



5 016 



4.997 



4.984* 



4.976* 



Galena, 111. 



5.028 



5.015 



5.010 



5.010 





Cumberland, Eng. 



5.018 



4.814 









Arizona. 



5.015 



5.007 



4.996 



4,994 





Gilpin Co., Col. 



5.011 



5.009 



5.003 



4.995 





Linden Mine, Wis. 



5.004 



4.957 



4.718 







New York City. 



5.003 



4.998 



4.946 







French Creek, Penn. 



5.001 



4.997 



4.968 



4.940 





' Sitzungsb. k. Akad. Wiss., Wien, (1854), XII, 286. 

 ' Ztschr. d. geol. Ges., (1864), XVI, 267. 



