Original paper

Effect of the shape of fundamental particles on XRD characteristics of illitic minerals

Šrodoń, Jan; Elsass, Françoise

European Journal of Mineralogy Volume 6 Number 1 (1994), p. 113 - 122

30 references

published: Feb 4, 1994
manuscript accepted: Oct 19, 1993
manuscript received: Dec 23, 1992

DOI: 10.1127/ejm/6/1/0113

BibTeX file

ArtNo. ESP147050601011, Price: 29.00 €

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Abstract Chemical and electron-microscope data (Pt-shadowing and HRTEM) on monomineral illitic samples are used to show that XRD peak positions and peak intensities related to the swelling characteristics of the samples strongly depend on the size of the mixed-layer crystals, while the Kübler index (the half-height width of the 001 reflection) of the samples recorded in Na-form is related to the thickness of fundamental particles. The ability of fundamental particles to associate face-to-face into mixed-layer crystals depends on geometric factors: particles of a given thickness are more prone to form mixed-layer crystals inducing more smectitic XRD characteristics if they have flat surfaces, a large diameter and are not elongated. The variability of particle morphologies detected in natural samples explains the lack of a good correlation between the Kübler index and the parameters reflecting the swelling ability of illites such as the percentage of smectite layers or the Ir index of Srodon (1984). In swelling clays, the thickness of coherent scattering domains, calculated from the Kübler index by means of the Scherrer equation, is larger than the mean thickness of the fundamental particles


fundamental particlesillite crystallinityKübler indexmixed-layerillite/smectiteXRDTEM