Decomposition of Iron Pyrites. 387 



specimen of pyrite (from Germany). It is evident then that 

 citric acid may be used to distinguish pyrrhotite from pyrite.'*' 43 



In a letter experiment on the hitter mineral alone, in which it 

 was subjected to ''prolonged contact with the same solution at 

 the ordinary temperature of the workroom, say 60° to 70° Fahr.," 

 he found that even " pyrite showed decided evidence of de- 

 composition in eight days; one month later, the solution ac- 

 quired a reddish-yellow color and reacted for iron and sulphuric 

 acid." 44 



The powerful intervention of naturally acidified meteoric wa- 

 ters appears not to have been considered, in reference to the 

 mode of weathering of pyrites now under discussion, but seems to 

 be far more probably concerned in this alteration than the agent 

 suggested to Rose by the proximity of the dyke at Beresowsk — 

 aqueous vapor at elevated temperature. Percolating waters, 

 acidified with carbonic and organic acids, are universally distri- 

 buted and continuous in action, and the distribution of these 

 interesting limouite pseudombrphs is equally wide, and their 

 production apparently in constant progress. Another probable 

 mode of the formation of these pseudomorphs, by precipitation 

 in contact with solutions from a basic matrix, will be discussed 

 beyond, as well as the general subject of vitriolization, and the 

 important fact that a stable form of pyrite exists. 



Marcasite. 



Synonyms : radiated pyrites, white iron pyrites, cockscomb 

 pyrites, pyrite blanche, pyrite rayon nee, strahlkies, speerkies, 

 kamkies, leberkies, wasserkies, zellkies, binarkies, kirosite. 



The published analyses of this mineral, and determinations of 

 its density, are few, imperfect, and greatly scattered. It is be- 

 lieved that the best are presented below. 



4:i Ann. N. Y. Acad. Sci. (1877), I, 18. 



44 Proc. Am. Ass. Adv. Sci. (1882), XXXI, Pt. I, 271. 



