Chemical and Biological Weathering in Vermiculite from Transvaal
1969
Sawhney, B. L. | Voigt, G. K.
Transvaal vermiculite flakes were weathered in solutions of salts or acids as well as in nutrient solutions inoculated with water extracts of soils from hemlock (Tsuga canadensis) and tulip poplar (Liridendron tulipifera) forest stands. Morphological changes were studied with a microscope and the structural changes were determined by X-ray diffraction analysis, while the changes in chemical composition were estimated by an electron microprobe. Weathering of flakes proceeded from edges inward and produced a weathered zone parallel to the flake edges. However, the changes produced by salt solutions were different from those by acids and biological agents. Treatment with salt solution produced the expanded weathered zone with a 14A c-axis spacing as compared to 10A spacing of the unaltered zone. Electron microprobe analysis revealed that the salt treatment replaced the interlayer K ions by the hydrated cations of the salt. Treatment with acids or biological agents, on the other hand, produced a bleached and fragile weathered border that was amorphous to X-rays. Electron microprobe analysis showed that the bleached zone was depleted of Fe, Mg, and Al, besides the interlayer K ions; concentration of these cations decreased towards the extremity of the edge. The amorphous nature of the weathered zone is attributed to the loss of the unit cell periodicity resulting from the removal of a portion of the octahedral and tetrahedral cations.
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