X-ray diffraction (XRD) peaks in a low-angle diffraction section of clay minerals, especially those ofauthigenic origin, have broadening and tailing features in shape. Using the five basic parameters, peak position, peakheight, width, shape coefficient and asymmetry, to describe an XRD peak is more accurate, comprehensive and integratedthan using only 3 of them, position, height and width. Following the concept of the five basic parameters of an XRD peak,the program Decoform proposed in this study provides more information in mineralogical analyses by fitting actual XRDprofiles. In combination with the HW-IR plot, Decoform can be systematically and accurately used in the comprehensiveanalyses of crystallinity, domain size, lattice strain and quantitative phase. It is also of value for the geologicalinvestigations of diagenesis, metamorphism, basin maturity, structural stress field and so on.
This paper derives the physical meanings of peak position, peak width and height of an X-ray diffraction peak from the analyses of the Bragg’s equation, the Scherrer’s formula and the principle of peak intensity calculation. The geometric characteristics of an asymmetric peak are clarified by means of experiment. The relationships between peak shape and domain size/lattice strain have been verified by geological events. Therefore this paper integrates the physical meanings of all 5 basic parameters for an X-ray diffraction peak. Applications of these 5 parameters are exemplified.
