Bulk and Glycolated Clay XRD Analysis

Bulk and glycolated clay X-ray diffraction (XRD) analysis consists of two separate XRD analyses of the sample. The "bulk" portion is an XRD of the whole sample including rock grains, cements and clays. The “clay” portion of the analysis is an XRD on the <2μm size clay fraction of the sample, which is separated using the floatation method. This concentrates the clay and gives a more accurate measure of the ratios between the clays detected.

GR Petrology’s standard clay treatment is glycolation — treating the clay sample with glycol to expand the swelling clay component (e.g. smectite). Additional clay treatments that we provide include air drying clay samples (used in conjunction with glycolated clay results for more accurate speciation) and heating clay samples to 550°C (to break down kaolinite).

Elemental analysis is not normally performed with Bulk & Clay analysis, however, it can be added to complete the picture of the sample’s composition.

Rietveld Analysis

Rietveld Analysis is an improved method of quantifying the proportions of compounds in a sample. Normal XRD analysis uses the “peak height” to calculate the abundance of the various components present. Rietveld analysis uses the “area under the peak” which is more accurate, and particularly so with clays which have very broad peaks.

Diffractograms show the bulk sample (red) and clay fraction (blue). Note how the clay fraction (blue) shows much larger peaks for the clays, which allows more precise determination of their relative abundances.