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Stacking Faults in the Kaolin-Group Minerals: Defect Structures of Kaolinite

Published online by Cambridge University Press:  02 April 2024

A. Plançon
Affiliation:
Centre de Recherche sur les Solides à Organisation Cristalline Imparfaite and Université d'Orléans, 45100 Orléans, France
R. F. Giese Jr.
Affiliation:
Department of Geology, State University of New York at Buffalo, 4240 Ridge Lea Road, Amherst, New York 14226
R. Snyder
Affiliation:
New York State College of Ceramics, Alfred University, Alfred, New York 14802
V. A. Drits
Affiliation:
Geological Institute, Academy of Sciences of the U.S.S.R., Pyzevsky 7, Moscow, U.S.S.R.
A. S. Bookin
Affiliation:
Geological Institute, Academy of Sciences of the U.S.S.R., Pyzevsky 7, Moscow, U.S.S.R.
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Abstract

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Previous studies of the defect structure of kaolinite have examined samples having a restricted level of defects. This study examined nine kaolinite samples having a large diversity of defect contents, as indicated by Hinckley indexes ranging from 1.44 to 0.18. The samples were chosen so as to cover this range in as regular a manner as possible. The types and abundances of the defects were determined by examining the X-ray powder diffraction profiles for the 02,11 and 20,13 bands. The diffraction intensities were measured by counting for a fixed time in steps of 0.01°2θ. Analysis of these diffraction profiles indicated that (1) the major defect is the existence of a translation between adjacent layers, which is not the usual (approximately a/3), but is related to that translation by the pseudo-mirror plane coincident with the long diagonal of the unit cell; (2) the existence of a few C layers among the B layer stacking is a minor defect; (3) many of the samples could be accurately modeled only by assuming the existence of two kaolinite phases; (4) the existence of only a few C layers in some samples does not support the idea of a continuous series from kaolinite to dickite through disordered intermediates; and (5) the Hinckley indexes of several samples depend on the relative proportions of the two types of kaolinite in the mixture.

The nine kaolinite samples fall into three groups: those having a low to moderate abundance of defects (Hinckley index > 0.43) are mixtures of two types of kaolinite (one almost free of defects, the other richer in defects); those having low Hinckley indexes (0.43 to 0.18) are single phases with different proportions of defects; and those which contain a single type of kaolinite, unlike the others in the nature of the interlayer translations and the greater abundance of C layers. The agreement between calculated and observed X-ray diffraction profiles is excellent for all specimens, except one sample (from Charentes) for which the fit is acceptable but not perfect.

Résumé

Résumé

Les précédentes études des défauts structuraux de la kaolinite ont porté sur des échantillonnages restreints. Dans cette étude, ont été examinés neuf échantillons de kaolinite présentant une large diversité dans l'abondance des défauts, et choisis de façon à couvrir, de manière aussi régulière que possible, le domaine de variation de l'indice d'Hinckley (de 1,44 à 0,18). Les types et abondances des défauts ont été déterminés à partir des bandes 02,11 et 20,13 d'enregistrements de diffraction X de poudres. Les intensités ont été enregistrées en pas à pas, avec un pas de 0,01°T, et un comptage à durée constante. L'analyse des profils de diffraction indique que: (1) le principal défaut est l'existence d'une translation entre feuillets adjacents qui n'est pas la translation habituelle (approximativement -a/3), mais celle qui s'en déduit par le pseudo miroir passant par la grande diagonale de la maille élémentaire; (2) l'existence de feuillets C, au sein des empilements majoritairement composés de feuillets B, est um défault mineur; (3) la plupart des écantillons ne peuvent être correctement modélisés que si l'on suppose l'existence de échantillons ne conforte pas l'idée d'une série continue allant de la kaolinite à la dickite, via les intermédiaires que seraient les kaolinites désordonnées; et (5) l'indice d'Hinckley de plusieurs échantillons dépend de la proportion des deux types de kaolinites dans les mélanges.

Les neuf échantillons de kaolinite se répartissent en trois groupes: ceux du premier groupe, qui ont une faible ou moyenne abondance de défauts (indice d'Hinckley >0,43), sont des mélanges de deux types de kaolinites (l'une presque sans défauts, l'autre riche en défauts); ceux du second groupe, qui ont un faible indice d'Hinckley (0,43 à 0,18), sont monophasés avec différentes proportions de défauts; le troisième groupe contient un seul echantillon, qui se distingue des autres par la nature de la translation entre feuillets et par la plus grande abondance en feuillets C. L'accord entre les intensités de diffraction expérimentales et calculées est exellent pour tous les énchantillons, excepté celui du troisième groupe, pour lequel l'accord est acceptable, mais non parfait

Type
Research Article
Copyright
Copyright © 1989, The Clay Minerals Society

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