Layer-stacking sequences and structural disorder in mixed-layer illite/smectite: Image simulations and HRTEM (high-resolution transmission electron microscopy) imaging

Journal Article · · American Mineralogist; (USA)

OSTI ID:6299005

Ahn, Jung Ho; Buseck, P R ^[1]

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1. Arizona State Univ., Tempe (USA)

R1- and R3-ordered mixed-layer illite/smectite (I/S) samples with 10, 18, and 30% expandable layers were investigated by high-resolution transmission electron microscopy (HRTEM) at 400 kV. In both R1 and R3 I/S samples, 1M{sub d} stacking dominates; in many crystals, stacking faults limit 1M order to only two or three layers. Although a high degree of stacking disorder largely accounts for 1M{sub d} characteristics as seen in X-ray diffraction patterns, HRTEM images indicate that individual 2:1 layers of I/S have slightly different {beta} values. Such structural heterogeneity of individual layers also contributes to the weakness or absence of hkl reflections. In one R3 I/S crystal (with 10% expandable layers), localized 2M{sub 1}-like stacking occurs within a disordered stacking sequence. Simulated images show significant differences between illite and smectite interlayers, but they cannot be differentiated in experimental images. Although the concept of fundamental particles (Nadeau et al., 1984a, 1984b, 1984c) implies that 20- and 40-{angstrom}-thick particles dominate in R1 and R3 I/S, respectively, consistent packet thicknesses showing the characteristics of fundamental particles are not observed in our specimens. All structure images show regions with coherent stacking, most of which are at least two or three times thicker than the predicted fundamental particles of Nadeau and coworkers. This observation supports the suggestion of Ahn and Peacor (1986b) that thin fundamental particles are secondary crystallites derived from larger crystals by cleaving at smectite interlayers during sample preparation.

• OSTI ID: 6299005
• Journal Information: American Mineralogist; (USA), Vol. 75:3-4; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
58 GEOSCIENCES
ILLITE
CRYSTAL STRUCTURE
SMECTITE
ENVIRONMENTAL TRANSPORT
LAYERS
METAMORPHIC ROCKS
MICROSTRUCTURE
MIXING
PETROLEUM
PETROLEUM DEPOSITS
RESERVOIR FLUIDS
RESERVOIR PRESSURE
SEDIMENTARY ROCKS
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
CLAYS
COHERENT SCATTERING
DIFFRACTION
ELECTRON MICROSCOPY
ENERGY SOURCES
FLUIDS
FOSSIL FUELS
FUELS
GEOLOGIC DEPOSITS
MASS TRANSFER
MICROSCOPY
MINERAL RESOURCES
MINERALS
OXYGEN COMPOUNDS
RESOURCES
ROCKS
SCATTERING
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
360602* - Other Materials- Structure & Phase Studies
580000 - Geosciences