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PKOCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 69 



All the postulates upon which Caspar! bases his conclusions as to 

 the colloidal nature of glauconite are partly or wholly wrong. Clays 

 contain varying proportions of minerals of colloidal size, and in 

 many the amount of colloidal material that can be identified is 

 small.^^ It is quite incorrect to assume that clays are wholly colloi- 

 dal or even predominantly colloidal as he seems to do when he refers 

 to "colloidal minerals (i. e. clay)." Again colloids are not neces- 

 sarily noncrystalline, for most colloids are finely dispersed crystalline 

 material. The crystallinity of most colloids has been emphasized 

 by Svedberg who says,^* " almost all particles in colloids are small 

 crystals," and this is undoubtedly the condition of the alkali and acid 

 treated material investigated by Caspari. Adsorption (the absorption 

 of Caspari) of water is a function of great surface area and does not 

 necessarily denote colloidal form, and a finely divided micaceous 

 material like glauconite has tremendous surface area and thus pos- 

 sesses the structure most conducive to great adsorptive powers, for 

 adsorption is not a property that suddenly springs into existence as 

 soon as the degree of subdivision reaches lOO/x/x which has been set 

 arbitrarily as the upper limit for colloidal size. 



Thus Caspari's conclusion that glauconite is a noncrystalline col- 

 loid has little to stand upon especially as he chose to disregard 

 properties like pleochroism and birefringence which he observed 

 and recorded, and to base his conclusions entirely upon erroneous 

 postulates and a faulty reasoning. There is nothing in the data 

 cited to indicate that glauconite is not an ordinary crystalline silicate 

 that contains much adsorbed water. 



The most thorough chemical study of glauconite that has been 

 published is that by Hallimond,^' of which the essential parts are 

 given below : 



In Table III is given the molecular proportions of 12 analyses of glauconite 

 and a comparision of these ratios leads to the following conclusion : 



13 Searle, Alfred B., The chemistry and physics of clays, pp. 263-269, Ernest Been, Ltd.. 

 London, 1924. 



" Svedberg, Theo, Chemical Review, vol. 1, 1924, p. 629. 



« Hallimond, A. F., Mineralogical Magazine, vol. 19, No. 98, pp. 332-333. 1922. 



