A Precise and Accurate Method for the Quantitative Determination of Carbonate Minerals by X-Ray Diffraction Using a Spiking Technique

H. A. Gunatilaka and Roger Till
Sedimentology Research Laboratory, University of Reading, Reading, RG6 2AB, England

Summary: A precise and accurate X-ray diffraction method has been developed whereby the weight percentages of aragonite and low- and high-magnesium calcite are determined from the integrated peak areas of spiked and unspiked samples. The spike mixture was prepared from organisms extracted from the samples to be analysed. Use of a spiking method also avoided the preparation of working curves from artificial mixtures of carbonate minerals, which may not have the same diffraction behaviour as the unknowns. A test of the precision of the method indicates the following coefficients of variation: aragonite, 1·4 %; low-magnesium calcite, 1·5 %; high-magnesium calcite, 7·8 %. A test of the accuracy of the method indicates no significant bias in any of the carbonate results, except in samples where high-magnesium calcite values are below 10 %. Quartz may also be determined by this method (coefficient of variation 23·9 %; positive bias in values greater than 10 %).

Mineralogical Magazine; December 1971 v. 38; no. 296; p. 481-487; DOI: 10.1180/minmag.1971.038.296.10
© 1971, The Mineralogical Society
Mineralogical Society (www.minersoc.org)