Special Techniques: Small pieces of the plastic polaroid can be used with 

 the ordinary low-power binocular microscope to serve the same purpose as nicol 

 prisms in the petrographic microscope. Place one piece beneath the stage of the 

 microscope where the light to the specimen will pass through it. The second 

 piece is inserted between the thin section and the objective lenses. A small wire 

 holder can be attached to the microscope to which the upper piece of polaroid 

 is fastened. When used only occasionally, the upper polaroid sheet may be 

 held in the right position in the hand. The specimens must be in the form of 

 thin sections. 



A small magnet may be used to remove magnetic grains from disaggregated 

 sandstones. Some black hematite is identical to magnetite in appearance, but 

 the two are easily separated with the magnet. After the magnetite has been 

 removed, the sample can be heated, then cooled, after which the hematite 

 becomes temporarily magnetic and can be removed with the magnet. 



In the study of carbonate rocks it is sometimes desirable to obtain a polished 

 section, even though the majority of determinations do not require this type of 

 examination. Lapping wheels and other necessary equipment are usually not 

 available. A polished section can be made very quickly from a sample chip with 

 a few pieces of inexpensive equipment consisting of the following: 



Geared emery grinding wheel, hand-operated, home-shop type, that can be 

 clamped on the edge of a table. 



Abrasive 4-inch wheels of about 80 to 150 grit. 



Plate glass 14 inch thick and 5 inches square. 



A few sheets of wet or dry emery paper of 150 to 400 grade. 



Hard sealing wax. 



Dowel pin 5/ 8 inch diameter and a few inches in length. 



Light machine oil. 



Model airplane "clear dope." 



A small amount of heated sealing wax is placed on the end of the dowel 

 pin. The wax is reheated and the chip is pressed down firmly into the soft wax 

 on the end of the stick. The chip is now ground to a plane on the side of the 

 emery wheel and polished on the emery paper to the necessary degree of fineness. 

 The emery paper is held on the glass plate when the specimen is ground. Either 

 oil or water may be used in the final grinding. A thin coat of "clear dope" on 

 the plane surface will bring out detail so that a high degree of polishing is not 

 necessary. The wax is reheated to remove the chip. 



A rough plane surface can be made quickly with a fingernail file or a 

 small, fine machinist's file. The chip is not difficult to hold if placed on a flat 

 pencil eraser. File marks are removed with fine emery paper. 



Several stain tests been developed to differentiate the main groups of clay 

 minerals: illite, montmorillonite, and kaolinite. Most of the tests are very 



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