examining. If no stain reaction is noted, a periodic examination should be made 

 up to about 2 hours for any characteristic color change. In the safranine "y" 

 and malachite-green tests, the sample should be examined between 2 and 10 

 minutes after the dye has been added. After about 10 minutes, the stained 

 particles may darken and become opaque, making the interpretation difficult. 



The characteristic results of these staining tests are summarized in Table 6- 

 III, prepared by Mielenze, King, and Schieltz (1951) . These tests are quite sensi- 

 tive, and it is recommended that trial tests be made on samples accurately 

 identified by X-ray diffraction. 



TABLE 6-III 



Characteristic Staining of Clay Minerals 

 (Mielenze, King, and Schieltz, 1951) 



*Dye absorbed without change in color. Samples of nontronite included with the clay 

 mineral standards did not change the color of the dyes in these tests, but specimens of 

 nontronite reacting in a manner similar to montmorillonite, have been examined in the 

 petrographic laboratory. 



**No beidellite is included in the clay mineral standards; beidellites examined in the 

 petrographic laboratory typically react in the staining tests, as does montmorillonite. 



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