Quantitative X-Ray Diffraction (XRD) Analysis Of Clay-Bearing Rocks From Random Preparations

QUANTITATIVE X-RAY DIFFRACTION ANALYSIS OF CLAY-BEARING
ROCKS FROM RANDOM PREPARATIONS

JAN S´RODON´ 1,3,*, VICTOR A. DRITS2,3, DOUGLAS K. MCCARTY3, JEAN C.C. HSIEH3 AND DENNIS D. EBERL41

 Permanent address: Institute of Geological Sciences PAN, Senacka 1, 31–002 Krako´w, Poland 2 Permanent address: Institute of Geology RAN, Pyzevskij 7, 109017 Moscow, Russia 3 Texaco Upstream Technology, 3901 Briarpark, Houston, TX 77042, USA
4 U.S. Geological Survey, 3215 Marine St., Boulder, CO 80303-1066, USA

Abstract—An internal standard X-ray diffraction (XRD) analysis technique permits reproducible and
accurate calculation of the mineral contents of rocks, including the major clay mineral families: Fe-rich
chlorites 1 berthierine, Mg-rich chlorites, Fe-rich dioctahedral 2:1 clays and micas, Al-rich dioctahedral
2:1 clays and micas, and kaolinites. A single XRD pattern from an air-dried random specimen is used.
Clays are quantified from their 060 reflections which are well resolved and insensitive to structural
defects. Zincite is used as the internal standard instead of corundum, because its reflections are more
conveniently located and stronger, allowing for a smaller amount of spike (10%). The grinding technique
used produces powders free of grains coarser than 20 mm and suitable for obtaining random and rigid
specimens.
Errors in accuracy are low, ,2 wt. % deviation from actual values for individual minerals, as tested
on artificial shale mixtures. No normalization is applied and thus, for natural rocks, the analysis is tested
by the departure of the sum of the measured components from 100%. Our approach compares favorably
with other quantitative analysis techniques, including a Rietveld-based technique.
Key Words—Clay Minerals, Marls, Quantitative Analysis, Shales, X-ray Diffraction..