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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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Three independent errors affect X-ray diffraction estimates of dolomite in pre-Cenozoic carbonate rocks. If calcite: dolomite main-peak [104] ratios are used, each 1% of excess calcium in the dolomite lattice causes a 2% overestimate of the amount of dolomite. Use of the second-intensity [113] ratios avoids the stoichimetry problem, but the [102] quartz peak (2.282A) interferes with the [113] calcite peak (2.282A). Where more than 20% quartz is present, the dolomite proportion in the sample may be seriously underestimated. The third source of error is due to difference between the crystallite size in the standards used to prepare the calibration curves and the crystallite size in the sample unknowns. These three errors can be avoided or corrected; however, point count of tained thin sections, a simple reliable technique, is preferable for analysis in most cemented carbonate rocks.
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