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Quantitative Determination of Clay Mineral Mixtures by X-Ray Diffraction¹

ABSTRACT

The quantitative determination of clay minerals by X-ray diffraction procedures was investigated using MgO as an internal standard. The determination of intensity constants for the 001 diffraction lines of samples of illitic, kaolinitic, and montmorillonitic types of clay was made with reference to the 1.48 Å MgO diffraction line. These constants were calculated using the integrated intensity of the specified diffraction lines, the known weights of clay and MgO in each sample, and the calculated value for the intensity of the MgO line. For kaolinitic and illitic types of clay the constants were evaluated with less than 2% average deviation, whereas for the montmorillonitic types the average deviations varied from 2 to 5%, depending upon the clay sample used. The values of the constants vary quite markedly from one species of clay mineral to another within each general clay type and, therefore, constants must be determined for each of the various clay species when they occur in a sample to be investigated.

From the intensity constants for the 001 diffraction lines of each clay specie present in a mixture and the integrated intensity of the respective lines, the percentage composition of known synthetic mixtures of two and three components was determined with an average deviation of 1.87% from the actual composition. It was found that clay constituents appearing in quantities less than 10% by weight gave considerably larger deviations, and in the case of such small quantities of illitic types, the diffraction line often could not be differentiated from the background radiation.

¹ Contribution No. 557, Department of Agronomy, and No. 62, Department of Physics, Kansas Agr. Exp. Sta., Manhattan. Portion of a dissertation to be presented by the senior author as partial fulfillment of the requirements for the Ph.D. degree in Agronomy at Kansas State College. Presented before Div. II, Soil Science Society of America, Cincinnati, Ohio, Nov. 14, 1956.

² Graduate Research Assistant, Physicist, and Associate Agronomist, respectively.

Received for publication July 20, 1956. Accepted for publication January 4, 1957.