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Three-Dimensional Structural Analysis of Altered Micas by Ion Beam/Scanning Electron Microscopy (FIB/SEM Dual Beam), µ-X-ray Diffraction, and Transmission Electron Microscopy


EMSL Project ID
29791

Abstract

Micaceous minerals such as biotite [K(Mg,Fe)3AlSi¬O10(F,OH)2] and muscovite [KAl2(AlSi3O10)(F,OH)2] are ubiquitous components of detrital sediments, including the soils at the Hanford Site in southeastern Washington. The T-O-T mica mineral structure consists of layered aluminosilicates where sheets of tetrahedrally coordinated silicon sandwich octahedrally coordinated aluminum. Trivalent substitutions for Si4+ (e.g., Al3+) and divalent substitutions for Al3+ (e.g., Fe2+) cause structural negative charge imbalances which are compensated by interlayer K+, binding the aluminosilicate sheets into mica books, deposited as mineral flakes in clastic sediments. Weathering in the sediment column in the presence of migrating solutions can cause the breakdown of the crystal structure to form reactive domains on the mica surface and within the flake interiors.

Project Details

Start Date
2008-07-30
End Date
2009-03-04
Status
Closed

Team

Principal Investigator

Bruce Arey
Institution
Pacific Northwest National Laboratory

Team Members

James McKinley
Institution
Pacific Northwest National Laboratory

Ponnusamy Nachimuthu
Institution
Environmental Molecular Sciences Laboratory