Effect of Temperature, Acidity, etc. 



427 



IV. Natukal Genesis of the Sulphides of Iron and Zinc. 



In the beginning of this paper, it was stated that former 

 experiments of the authors showed that only the stable forms 

 of the sulphides of iron (FeS 9 ), zinc (ZnS), and mercury (HgS), 

 viz : pyrite, sphalerite, and cinnabar, could be obtained from 

 alkaline solutions, and the . corresponding unstable forms, 

 marcasite, wurtzite and meta-cinnabar (?) had only been 



Fig. 5. 



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CM 



* 3 

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c 



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s. z 

























































fi 





























/ 



r 



























/ 



/ 



























A 



t 





sP 













wu 



rt: 



:ite 













/ 



/* 







































































^K 















SPh 



IAL 



1RT 



■E 















c< 























200 250 300 350 



Temperature 



Fig. 5. Fields of precipitation of sphalerite and wurtzite. 



obtained from acid solutions. A revision of a portion of that 

 work in the present paper confirms the former results. Some 

 new evidence bearing on the genesis of several of these 

 minerals in nature has recently been brought to our attention. 

 Our experiments on the formation of pyrite from alkaline 

 solutions extended from 300° down to 70°. Pyrite had also 

 been observed as a product of alkaline waters in nature at a 

 temperature of 55°.* Evidence is now at hand which proves 

 that from cold alkaline solutions also, pyrite and not marcasite 

 is obtained. 



A. Pyrite from cold alkaline solutions. — Mr. C. E. Sieben- 

 thal,f of the U. S. Geological Survey, has made observations 

 on a number of springs in which it can hardly be doubted 

 that pyrite is now forming. These are the "White Sulphur" 

 and "Black Sulphur" occurring in the town of Sulphur Springs, 

 Arkansas. Both contain a dark sediment which has separated 



* In the Carlsbad Springs. See Daubree, Geologie experimentale, p. 93 

 (Paris, 1879). 



f Bull. U. S. Geol. Survey 606, Origin of the Joplin Lead and Zinc Deposits. 

 In preparation. 



