Structural Heterogeneity and “Crystallinity” Indices of Natural Kaolinites

Abstract

To overcome the existing uncertainty in the interpretation of “crystallinity” indices of kaolinites, HI [Hinckley, 1963], IK [Stoch, Sikora, 1966; Stoch, 1974], QF [Range, Weiss, 1969], AGFI [Aparicio, Galán, 1999; Aparicio et al., 2006], WIRI [Chmielová, Weiss, 2002], their values obtained for a representative collection of 30 kaolinite samples were compared with the results of modeling the corresponding X-ray diffraction patterns. It is shown that all the studied samples consist of a mixture of almost defect-free high ordered HOK and defective low-ordered LOK kaolinite phases, and that there are relationships between the HOK content and the values of the “crystallinity” indices, which are described by different regression equations. The relationship is most pronounced for HOK and the Hinckley index, HI, which is described by the quadratic equation HOK (%) = 12.236 HI2 + 25.464 HI ‒ 1.2622 with the correlation factor R2 = 0.993. The resulting equations can be used to find concentrations of HOK and LOK in natural kaolinites. Comparison of structural parameters of defective kaolinites obtained by modeling of their X-ray diffraction patterns with those of Expert System [Plançon, Zacharie 1990] showed that the latter sometimes predicts: 1) single-phase highly defective kaolinites, while their diffraction pattern modeling establishes a mixture of HOK and LOK phases; and 2) in two-phase samples, the content of the low-defect phase (ldp) is greater than 100%.