exacting and require more equipment than is normally available to the well- 

 sample examiner. All clay-stain tests demand a great deal of care; none is 

 infallible. The tests are often confused by mixtures of more than one mineralogi- 

 cal type, and in some cases are difficult to interpret because of the absorptive 

 properties of clays. 



The following test is comparatively simple, is fairly reliable, and does not 

 require special apparatus. The reagent is benzidine hydrochloride, which has 

 a pink color. When this stain is applied to kaolinite, there is no color change. 

 When it is applied to bentonite or illite clays, the color changes to blue. A 

 number of impurities, including gypsum, interfere with the test. 



Another test, which requires acid treatment of the specimen, employs a 

 solution of 25 cubic centimeters of nitrobenzene and 0.1 gram of crystal violet. 

 The solution is vivid purple. 



First the clay is boiled in strong hydrochloric acid for at least 30 minutes; 

 then it is washed thoroughly in distilled water, and in clean water two or three 

 times. The specimen is dried at about 105C, and the solution is applied. 

 Kaolinite simply absorbs the purple stain; illite turns dark green; and mont- 

 morillonite first stains green, then changes to greenish-yellow or orange. 



RECORDING THE DATA The descriptions of well samples should ad- 



here to a definite style or pattern. Written 



Descriptions of Well Samples descriptions are much easier to plot if the 



name of the rock is given first; then the 



various characters should be described in a consistent order. When this plan 



is followed, it is more convenient to compare like characters of the different 



lithologic units. 



Example : 



Ss — 0.1 mm, angular, compact, muscovite, buff. 

 Ss — 0.5 to 0.9 mm, round, friable, glauconitic, red. 

 Ls — 0.5 mm, oolitic, argillaceous, tight, dark gray. 

 Dolo — 0.2 mm, rhombic, sandy (0.1 mm) , brown. 

 Sh — red-brown, fissile, calcareous, micaceous. 

 Sh — dark gray, lumpy, silty, biotite, pyrite. 



Typewritten logs made from the written descriptions of the microscopist 

 have the advantage of being easily reproduced if a number of copies are needed. 



Plotted Interpretive Logs 



There is a considerable difference of opinion on whether the strip log 

 should be plotted concurrently with the examination of samples or whether notes 



42 



