Subsurface Laboratory Methods 



127 



Slaking and swelling in water — Useful in differentiating clay-mineral 

 groups. Kaolins ordinarily do not slake. Very marked slaking and swell- 

 ing differentiate some bentonites from other bentonites and illites. 



Smell — Earthy smell suggests kaolin; no smell suggests illites and 

 montmorillonites. 



In cores the identification of minerals is the same as in other hand 

 specimens. It is possible, however, to bring out structures and textures 



LIMESTONE' 



( DOLOMITE ) 



SANDY (SILTY) 

 LIMESTONE 

 (DOLOMITE) 



SHALY LIMESTONE 

 (DOLOMITE) 



LIMY (DOLOMITIC) 

 SANDSTONE 

 (SILTSTONE) 



SANDSTONE 



(SILTSTONE) 



SHALY 



SANDSTONE 



{ SILTSTONE) 



SANDY (SILTY) 

 SHALE 



LIMY (DOLOMITIC) 

 SHALE 



SHALE 



Figure 53. Classification of the common-sedimentary rocks. (Modified from Pirsson 



and Scliucfiert.) 



of cores by preparing a polished section that can be examined mega- 

 scopically or when wet with a binocular microscope. By using a carborun- 

 dum stone or carborundum powder on a glass plate, one can quickly pre- 

 pare such polished sections. 



Texture 



Texture which may be defined as the intimate grain-to-grain relation- 

 ships of a rock, represents the sum total of such properties as grain-size 

 distribution, grain shape and roundness, fabric, pore shape, and cementa- 

 tion, as distinguished from mineralogic composition. Composition, in so 

 far as it controls or partly controls the other properties, may be consid- 

 ered a factor in texture. 



