Powder X-ray diffraction analysis of homogeneous and heterogeneous sedimentary dolostones

The %Ca (molar Ca/(Ca + Mg) X 100) in sedimentary dolomite, which ranges fr om 48 %Ca to 62.5 %Ca, can be determined by atomic absorption spectrometry, electron microprobe analysis, or powder X-ray diffraction analysis. The la tter procedure, which relies on the fact that the position of the d(104) re flection depends linearly on the Ca content, offers an easy and relatively inexpensive method of determining %Ca in dolomite. To date, such analyses h ave assumed that the dolostone is homogeneous with respect to the %Ca conte nt of its constituent dolomite crystals. Herein, the XRD technique is exten ded to compositionally heterogeneous dolostones. A considerable amount of important information can be derived from X-ray di ffractograms of dolostones if they are analyzed with peak-fitting technique s (PF-XRD). Specifically, this technique allows (1) determination of the %C a with an accuracy of +/- 0.5 %Ca, (2) identification of heterogeneous dolo stone samples formed of more than one population of dolomite crystals as de fined by their %Ca content, and (3) derivation of the proportion of each po pulation of dolomite crystals with an accuracy of +/- 10%. The PF-XRD techn ique is a powerful analytical tool that provides valuable information on th e major-element composition of low-Fe dolomite. Compared to other technique s, the PF-XRD technique is accurate, rapid, relatively inexpensive, and eas y to use.