Nontronite: chemistry and x-ray diffraction

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Abstract
Chemical and X-ray analysis of eight samples of nontronite are consistent with the Hofmann et al. montmorillonite structure. The finest fraction of some fully hydrated (15·3 Å) samples is composed of crystals all about 6 or 7 unit cells thick, and having 12 H2O per 8 Si, arranged at three levels in the interlayer, possibly as upright octahedra. During dehydration, non-integral 00l sequences, and variations in d001 result from a range of layer thickness in one crystal, caused by loss of water from the crystal periphery with consequent margin collapse. At about 50% relative humidity, the H2O content of nontronite is determined by the tetrahedral aluminium, probably because Aliv controls maximum crystal size.