Evolution of Fundamental-Particle Size during Illitization of Smectite and Implications for Reaction Mechanism

Area-weighted thickness distributions of fundamental illite particles for samples of illite and illite-smectite from seven locations (including bentonites and hydrothermally altered pyroclastics) were measured by Pt-shadowing technique, by transmission electron microscopy. Most thickness distributions are described by lognormal distributions, which suggest a unique crystallization process. The shapes of lognormal distributions of fundamental illite particles can be calculated from the distribution mean because the shape parameters α and β2are interrelated: β2= 0.107α − 0.03. This growth process was simulated by the mathematical Law of Proportionate Effect that generates lognormal distributions. Simulations indicated that illite particles grow from 2-nm thick illite nuclei by surface-controlled growth, i.e., the rate of growth is restricted by how rapid crystallization proceeds given a near infinite supply of reactants, and not by the rate of supply of reactants to the crystal surface. Initially formed, 2-nm thick crystals may nucleate and grow within smectite interlayers from material produced by dissolution of single smectite 2:1 layers, thereby transforming the clay from randomly interstratified (Reichweite, R = 0) to ordered (R = 1) illite-smectite after the smectite single layers dissolve. In this initial period of illite nucleation and growth, during which expandable layers range from 100 to 20%, illite crystals grow parallel to [001]* direction, and the dimensions of the (001) plane are confined to the size of the original smectite 2:1 layers. After nucleation ceases, illite crystals may continue to grow by surface-controlled growth, and the expandable-layer content ranges from 20 to 0%. This latter period of illitization is characterized by three-dimensional growth. Other crystal-growth mechanisms, such as Ostwald ripening, supply-controlled growth, and the coalescence of smectite layers, do not produce the observed evolution of α and β2and the observed shapes of crystal thickness distributions.

[1]  J. Cuadros,et al.  Characterization of mixed-layer illite-smectite from bentonites using microscopic, chemical, and X-ray methods: Constraints on the smectite-to-illite transformation mechanism , 1998 .

[2]  D. Eberl,et al.  Deducing growth mechanisms for minerals from the shapes of crystal size distributions , 1998 .

[3]  D. Eberl,et al.  XRD Measurement of Mean Thickness, Thickness Distribution and Strain for Illite and Illite-Smectite Crystallites by the Bertaut-Warren-Averbach Technique , 1998 .

[4]  D. Eberl,et al.  Measurement of Fundamental Illite Particle Thicknesses by X-Ray Diffraction Using PVP-10 Intercalation , 1998 .

[5]  S. Altaner,et al.  Comparison of Structural Models of Mixed-Layer Illite/Smectite and Reaction Mechanisms of Smectite Illitization , 1997 .

[6]  N. Clauer,et al.  K-Ar dating of illite fundamental particles separated from illite-smectite , 1997, Clay Minerals.

[7]  D. Eberl,et al.  XRD Measurement of Mean Crystallite Thickness of Illite and Illite/Smectite: Reappraisal of the Kubler Index and the Scherrer Equation , 1997 .

[8]  István Viczián.  Hungarian Investigations On The “Zempleni” Illite , 1997 .

[9]  M. Tóth,et al.  TEM and XRD determination of crystallite size and lattice strain as a function of illite crystallinity in pelitic rocks , 1997 .

[10]  F. Elsass,et al.  Particle Shape versus Coherent Scattering Domain of Illite/Smectite: Evidence from HRTEM of Dolná Ves Clays , 1996 .

[11]  R. Kitagawa,et al.  Morphological characteristics of illitic clay minerals from a hydrothermal system , 1994 .

[12]  J. Petes,et al.  Smectite to Illite Conversion in Bentonites and Shales of the East Slovak Basin , 1993, Clay Minerals.

[13]  R. C. Reynolds.  X-Ray Diffraction Studies of Illite/Smectite from Rocks, < 1 μm Randomly Oriented Powders, and < 1 μm Oriented Powder Aggregates: The Absence of Laboratory-Induced Artifacts , 1992 .

[14]  F. Elsass,et al.  Chemistry of illite-smectite inferred from TEM measurements of fundamental particles , 1992, Clay Minerals.

[15]  D. Champion,et al.  The I/S-to-illite reaction in the late stage diagenesis , 1991 .

[16]  F. Elsass,et al.  Direct High-Resolution Transmission Electron Microscopic Measurement Of Expandability Of Mixed-Layer Illite/Smectite In Bentonite Rock , 1990 .

[17]  Jan Środoń,et al.  Ostwald Ripening of Clays and Metamorphic Minerals , 1990, Science.

[18]  B. Velde,et al.  Mechanism of illite formation during smectite-to-illite conversion in a hydrothermal system , 1988 .

[19]  D. Eberl,et al.  Ostwald ripening and interparticle-diffraction effects for illite crystals , 1988 .

[20]  R. Kirkpatrick,et al.  Evidence from 29Si NMR for the structure of mixed-layer illite/smectite clay minerals , 1988, Nature.

[21]  P. Nadeau.  Relationships between the mean area, volume and thickness for dispersed particles of kaolinites and micaceous clays and their application to surface area and ion exchange properties , 1987, Clay Minerals.

[22]  N. Kohyama,et al.  Chemical and Morphological Evidence for the Conversion of Smectite to Illite , 1987 .

[23]  DBNNTs D. EsnRL,et al.  Sericite from the Silverton caldera, Colorado: Correlation among structure, composition, origin, and particle thickness , 1987 .

[24]  M. R. Karlinger,et al.  Chemistry of Illite/Smectite and End-Member Illite , 1986 .

[25]  S. Jennings,et al.  Diagenesis of Plio-Pleistocene sediments of the Colorado River delta, Southern California , 1986 .

[26]  P. Nadeau.  The physical dimensions of fundamental clay particles , 1985, Clay Minerals.

[27]  J. M. Tait,et al.  Interstratified Clays as Fundamental Particles , 1984, Science.