Subsurface Laboratory Methods 



207 



lend itself to study in the electron microscope. This latter case leads into 

 the problem of the study of shales. 



Correlation of Clays 



Quoting from Hillier,^^*^ ". . . particles of various types of clay 

 have probably been subjected to more examination by means of the elec- 

 tron microscope than any other type of material." Some clays are com- 

 posed of grains of about fifty angstroms in thickness and a few ang- 

 stroms wide. Studies of the nature and correlation of such minute 



Figure 88. Electron-microscope picture of infusorial earth (X 20,000) sold by 

 Central Scientific Company, Chicago. Note that fibers and bundles of fibers are 

 very similar to those in photograph of Attapulgus clay in figure 87. Diatom 

 fragment near center of photograph is about l%.u in length by l|.i wide. Openings 

 in shell are less than % [j, in diameter (0.0002 mm.) and would barely be dis- 

 cernible in the light microscope. (Courtesy R.C.A. Laboratories and Standard 

 Oil Development Company.) 



particles in the electron microscope are dependent on characteristic shapes 

 and not on chemical combinations. 



One of the clays used extensively in laboratories and refineries for 

 filtering is called "Attapulgus clay," so named for Attapulgus, Georgia. 

 Chemical analyses of this clay show it to be chiefly montmorillonite, a 

 hydrous aluminum silicate, but the individual microcrystalline masses 

 cannot be identified or resolved under the best light microscope. Figure 

 87 is an electron-microscope picture of this clay, X 20,000, showing an 



'™ Hillier, J., Electron Microscopy: Am. Ceramic Soc. Bull., Nov. 1946. 



