XRD-based quantitative analysis of clay minerals using reference intensity ratios, mineral intensity factors, Rietveld, and full pattern summation methods: A critical review

The quantification of clay minerals is essential for the evaluation of clay-rich rock and soil, but it remains challenging due to the unique structures and various element compositions of clay minerals. In this article, several quantification methods for clay minerals sourced from X-ray diffraction (XRD) analysis, mainly recommending the reference intensity ratio (RIR), mineral intensity factor (MIF), Rietveld, and full pattern summation methods are reviewed. Principles and applications of these methods are focused upon in addition to related differences in the analysis of clay minerals (i.e., sample preparation, the selection of characteristic reflections for quantification and standards added during analysis). This critical review also provides a proposal for selection of an adaptive XRD quantification method to be applied to various clay-rich samples.