Quantitative analysis of carbonate sediments using powder X-ray diffraction and the Rietveld method

Conference · Wed Jan 01 00:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:6135535

Post, J E ^[1]

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1. Smithsonian Institution, Washington, DC (United States). Dept. of Mineral Sciences

Critical to most studies of carbonate sediments is information about the relative abundances of different carbonate minerals and the Mg mole-percent of the calcite phases. Traditional powder X-ray diffraction methods for extracting these data rely upon measurement of the integrated area and d-spacing of the 104 calcite peak. This approach, however, is difficult for diffraction patterns with severely overlapping peaks and is prone to a range of systematic errors. The Rietveld analysis method makes use of the entire powder X-ray diffraction pattern and can quickly yield accurate quantitative phase analysis (without the need for standards) and unit-cell parameters for even complex mixtures. Furthermore, corrections for certain systematic errors (e.g. sample displacement) are also refined, eliminating the need to add internal standards to the samples. The d-spacings, a, and c values from the refinement can be used with standard determinative curves for Mg mole-percent. Also, in many cases, the Rietveld refinement can yield directly the Mg composition of each calcite phase. Results from several prepared two and three phase carbonate mixtures will be shown to demonstrate the accuracy of the technique. Applications to natural samples of mollusk shells, coralline algae, echinoderm spines, and carbonate muds will also be discussed.

• OSTI ID: 6135535
• Report Number(s): CONF-921058-; CODEN: GAAPBC
• Journal Information: Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CARBONATE ROCKS
CHEMICAL ANALYSIS
CALCITE
COMPARATIVE EVALUATIONS
MAGNESIUM
MEASURING METHODS
MIXTURES
ALKALINE EARTH METALS
CARBONATE MINERALS
DISPERSIONS
ELEMENTS
EVALUATION
METALS
MINERALS
ROCKS
SEDIMENTARY ROCKS
580000* - Geosciences
400102 - Chemical & Spectral Procedures