Errors in X-ray Analysis of Carbonates Due to Solid-solution Variation in Composition of Component Minerals

摘要: ABSTRACT Determination by X-ray diffraction of the relative proportions component minerals in sediments and rocks involves comparison integrated intensity selected reflections from unknown mixture to standard calibration curves. Although analysis may be rapid precise, a number factors contribute poor accuracy. The role one these, variation chemical composition minerals, is not generally appreciated. Calculations intensities two principal calcite, magnesite, siderite, rhodochrosite, dolomite, ankerite, kutnahorite show that strongest reflection, {211} ({1014} referred hexagonal axes), highly sensitive isomorphous substitution cations. It reflection use for if there any significant mixture. One important example compositional magnesium calcium biogenic calcite Recent sediments. {210} ({1123} axes) second most compositions rhombohedral carbonates. practically independent solid-solution makes an ide l choice mixtures. Calibration curves involving internal mineral comprises more than about eight weight percent sample, will strong enough utilize. Solid-solution common extensive carbonate rocks. An investigator should aware its effect on before beginning analysis. recommended natural mixtures, with cerric oxide as standard.