: Paleoclimatology: smectite

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smectite

A smectite is a mineral mixtures of various swellable sheet silicates (phyllosilicates), which have a three-layer structure and belong to the clay minerals. Smectites consist mainly of montmorillonite, but also contain quartz and calcite dust. The three-layer structure consists of two tetrahedron layers which are electrostatically cross-linked via the cations of an octahedron intermediate layer. The layers are not rigidly connected to each other; they can swell due to the reversible incorporation of water and other substances. Smectite is produced by chemical weathering of feldspars in soils or possibly by authigenic formation in saline lakes as alteration products of volcanic materials (Jones and Weir, 1983). In particular, smectite is often an authigenic mineral formed from the weathering of basalt, but it also occurs on sediments and calcareous substrates. It occurs predominantly in drier climates and in landscapes with low relief. (Adapted from: https://en.wikipedia.org/wiki/Smectite and J. P. Bradbury (1997), Quaternary Science Reviews, Vol. 16, 203-219. and R. A. Viscarra Rossel (2011), Journal of Geophysical Research Atmospheres 116(F4) : F04023.)

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