Quantitative mineralogy of sandstones by X-ray diffractometry and normative analysis

Quantitative X-ray diffraction, normative calculation, and whole-reek chemi cal analysis have been compared for Permo-Triassic quartz-lithic to litho-f eldspathic sandstones from eastern Australia, The quantitative XRD techniqu e provides mineralogical percentages that correlate well with the chemical composition of the sandstones, and also with most of the mineral percentage s derived from normative calculation. The need far assumptions on potassium distribution between minerals provides a limitation on estimates of K-feld spar and illite using the normative technique, although these can be improv ed on a sample-specific basis if necessary using complementary thin-section observations or qualitative X-ray diffractograms, Quantitative XRD analysi s possibly indicates a small proportion of amorphous material in some of th e sandstones, especially materials with abundant lithic fragments or clay m inerals, but the proportion of any amorphous material overall is probably n egligible, Both quantitative XRD and normative calculation avoid problems a ssociated with sample heterogeneity or operator inconsistency that may affe ct point counting of thin sections, They can also be used to provide quanti tative information on sediments with abundant rock fragments or matrix comp onents, the actual mineralogy of which is not resolvable in conventional mi croscope investigations.