ABSTRACT

The %Ca (molar Ca/(Ca + Mg) 100) in sedimentary dolomite, which ranges from 48 %Ca to 62.5 %Ca, can be determined by atomic absorption spectrometry, electron microprobe analysis, or powder X-ray diffraction analysis. The latter procedure, which relies on the fact that the position of the d₁₀₄ reflection depends linearly on the Ca content, offers an easy and relatively inexpensive method of determining %Ca in dolomite. To date, such analyses have assumed that the dolostone is homogeneous with respect to the %Ca content of its constituent dolomite crystals. Herein, the XRD technique is extended to compositionally heterogeneous dolostones.

A considerable amount of important information can be derived from X-ray diffractograms of dolostones if they are analyzed with peak-fitting techniques (PF-XRD). Specifically, this technique allows (1) determination of the %Ca with an accuracy of ± 0.5 %Ca, (2) identification of heterogeneous dolostone samples formed of more than one population of dolomite crystals as defined by their %Ca content, and (3) derivation of the proportion of each population of dolomite crystals with an accuracy of ± 10%. The PF-XRD technique is a powerful analytical tool that provides valuable information on the major-element composition of low-Fe dolomite. Compared to other techniques, the PF-XRD technique is accurate, rapid, relatively inexpensive, and easy to use.