Domain segregation in Ni-Fe-Mg-smectites

The first stage of lateritic weathering of pyroxenes in the Niquelandia area, Brazil, leads either to Fe-rich products or to a phyllosilicate clay. In relatively unfractured parent rock the phyllosilicate clay contains Ni-rich smectites. Extensive studies suggest that in the smectites Ni, and perhaps some Mg, are clustered in pimelite-like layers, whereas Fe and some Al are clustered in nontronite-like layers. The particles seem to contain several stacked layers. The seemingly homogeneous Ni-Fe-Mg smectite actually consists of mixed trioctahedral and dioctahedral layers.