aluminum chloride, and 24 cubic centimeters of water. The mixture is brought 

 to a boil and cooled; then a small quantity of hydrogen peroxide is added. The 

 solution is then filtered and ready for use. Calcite will stain a dark purple 

 when immersed about 30 seconds in the solution, whereas dolomite remains un- 

 affected. Osborne (Australasian Petroleum Company) suggests doubling the 

 amount of haematoxylin and immersing the specimen for 5 to 10 minutes. He 

 also states that upon occasion the stain may be improved by holding the speci- 

 men over an open bottle of strong ammonia. The Fairbanks method is reliable 

 and fast because it is not necessary to boil the specimen in the solution. 



Copper Nitrate Method 



When boiled in a solution of copper nitrate, calcite is stained green, whereas 

 dolomite is unaffected. Ross (1935) suggests that the specimen be immersed 

 in a cold solution of copper nitrate for several hours. Rodgers (1940) recom- 

 mends a one-molar solution of copper nitrate and immersion for 5 hours at 

 room temperature. The color is fixed by immersing in ammonia. This test 

 gives good and consistent results. 



Silver Chromate Method 



In this method the specimen first is immersed 3 or 4 minutes in a hot (70C) 

 10-percent solution of silver nitrate, washed, and then placed in a saturated 

 solution of potassium chromate for about 1 minute. Calcite is stained reddish- 

 brown, whereas dolomite is unaffected. Weaker solutions of silver nitrate and 

 potassium chromate give a more delicate and selective test. Osborne suggests 

 that a 1 -percent solution of silver nitrate and a 2-percent solution of potassium 

 chromate be used. He also recommends that the sample be treated 1 minute in 

 a cold instead of a hot silver nitrate solution. 



Calcite and Aragonite 



A method of distinguishing aragonite from calcite was suggested by Meigen 

 (1901). The specimen is immersed for 20 minutes in a solution of boiling 

 cobalt nitrate. Aragonite stains a light purple in the initial stages and becomes 

 dark purple upon continued treatment. Calcite stains a similar color only after 

 several hours of immersion. 



Quartz and Feldspars 



It is often desirable to determine the percentages of quartz and feldspar in 

 a sediment, and it is usually time consuming to distinguish between the two by 

 petrographic procedure. A simple and reliable staining method first suggested 

 by Becke (1889) can be used effectively to distinguish between these two 

 minerals. Twenhofel and Tyler (1941) summarized this method as follows: 



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