GLAUCONITE 



J. K. PRATHER 

 Waco, Tex. 



The samples of glauconite were taken from the (Cretaceous) 

 Greensands of New Jersey. 1 



William B. Clark states that there are "two conditions necessary 

 in the development of glauconite (i) deposition of particles of land 

 derived origin, and (2) the presence of Foraminifera." 



Murray and Renard state: 



The chambers become filled with muddy sediment, and if we admit that the 

 organic matter inclosed in the shell and in the mud itself transforms the iron 

 into sulphide, which may be oxidized into hydrate, sulphur being at the same 

 time liberated, this sulphur would become oxidized into sulphuric acid, which 

 would decompose the fine clay, setting free colloid silica and hydrated oxide of 

 iron in a state most suitable for their combination. 



Leith says: 



It is difficult to see how so high a percentage of iron as is found either in 

 glauconite or greenalite can be derived from the decomposition of mud filtered 

 into the interior of the shell. The contents of metallic iron shown in the analysis 

 of the greenalite rock is 25 per cent. In the typical glauconite deposits foreign 

 material is present outside of the shells, and there seems to be no reason why all 

 this material should not be drawn upon for the supply of iron. 2 



He further states : 



Where iron is being contributed to ocean waters in considerable abundance, 

 it is possible to conceive of minute organisms abstracting the same and depositing 

 it directly in such form as glauconite or greenalite. 



The New Jersey glauconite was deposited in comparatively 

 shallow water, as is shown by the land-derived material present even 

 in the purest samples of glauconite, and the cross-bedding. 



In the glauconite I have studied, the casts of shells of Forami- 

 nifera seem to be the exception rather than the rule. The grains are 



1 See The Atlantic Highlands Section of the New Jersey Cretacic, American 

 Geologist, 1905. 



2 Monograph 43 of the U. S. Geological Survey: "The Mesabi Iron-Bearing Dis- 

 trict of Minnesota," pp. 254. 



Soo 



