When studying a large number of carbonate rock samples, the usual methods for determining the calcite or dolomite content are time-consuming and tedious. To identify and count grains in thin-section is difficult for the most experienced. If sections or powders of the rock are subjected to various stains or dyes grain counts, still, must be made. In working with the silver nitrate-potassium chromate method (Lemberg, 1892), the author noticed a definite difference in the colors produced in several samples of powdered limestone by the stain. In this method the calcite is stained a very dusky red, whereas the dolomite is unaffected. Therefore, it is obvious that the mass color of a powder will be related to the relative proportions of dolomite and calcite. On this basis, a set of eleven standard samples was prepared from mineralogically pure calcite and dolomite. These samples range from 100 percent calcite to 100 percent dolomite. Intervening samples are mixtures of calcite and dolomite varying in 10 percent increments. Each sample then underwent precisely the same staining procedure. The result is a series of powders varying in color from very dusky red, through several lightness values of grayish red and pale red, to light gray. The color names are those which appear in the Rock-Color Chart distributed by the National Research Council, 1948.
Proceedings of the Iowa Academy of Science
©1950 Iowa Academy of Science, Inc.
Lawson, Ralph W.
"Determination of Calcite-Dolomite Ratios in Carbonate Rocks,"
Proceedings of the Iowa Academy of Science, 57(1), 263-266.
Available at: https://scholarworks.uni.edu/pias/vol57/iss1/31