Subsurface Laboratory Methods 



173 



graphic miscroscope and (2) the binocular microscope. The former 

 makes use of polarized light for the identification of minerals and the 

 detailed study of thin sections, whereas the latter uses ordinary trans- 

 mitted or incident light and is normally used for observing the larger 

 features such as lithology, texture, and structure. 



Some rivalry appears to exist among workers as to the superior quali- 



FiGURE 72. Basic equipment required for preparing a rapid 

 heavy-mineral concentrate of a rock. 



ties of the two types of microscopes. Each type has its field of usefulness. 

 Numerous problems are solved most economically with the aid of both 

 kinds of microscopes. Any well-equipped microscopic laboratory should 

 contain both petrographic and binocular microscopes, and should have 

 trained technicians trained to operate them. 



On pages 119-120, Rittenhouse discusses some of the uses of the 

 binocular microscope on sedimentary rocks. His article deals primarily 

 with detrital mineralogy, whereas this paper is chiefly concerned with 

 thin-section investigation, although a rapid method of heavy-mineral sepa- 

 ration is presented. 



