Abstract
Chloritic veins in serpentinite and their weathering products were analyzed by X-ray powder diffraction (XRD) and X-ray fluorescence spectrometry (XRF). Chlorite formed during the Hercynian-age orogenesis had apparently been partly transformed to high-charge vermiculite during subsequent metamorphism of the rocks. The idealized structural formulae for these minerals are (Al1.9Fe3+0.2Fe2+0.4Mg9.2Cr0.2)(Si5.8Al2.2)O20(OH)16 and X1.3(Fe3+0.7Fe2+0.1Mg5.2Ni0.1)(Si5.8Al2.2)O20(OH)4, respectively. This transformation appears to have taken place by the removal of the hydroxy-interlayer from the chlorite without major effect on the rest of the structure. It is not clear whether other hydroxy-interlayered vermiculites containing less tetrahedral aluminum were intermediate weathering products or inherited minerals. The ultimate weathering product of chlorite and vermiculites was a Fe3+-rich smectite, which probably formed by precipitation from solution.
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Publication No. 926 of the Department of Soil Science and Geology.
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Buurman, P., Meijer, E.L. & van Wijck, J.H. Weathering of Chlorite and Vermiculite in Ultramafic Rocks of Cabo Ortegal, Northwestern Spain. Clays Clay Miner. 36, 263–269 (1988). https://doi.org/10.1346/CCMN.1988.0360308
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DOI: https://doi.org/10.1346/CCMN.1988.0360308