Experimental Evidence on the Origin of Vermiculite in Soils on Lower Palaeozoic Sediments

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Abstract
Vermiculite occurs as a pedogenetic product in soils on Lower Palaeozoic sediments in mid‐Wales. Iron‐rich chlorite and dioctahedral illite, both of which are present in these sediments, are possible precursors. Field evidence on the occurrence of vermiculite indicates an increase in vermiculite coincident with chlorite weathering and a maximum vermiculite content in moderately weathered horizons. The vermiculite content of highly weathered eluvial and organic horizons of podzols is low. Using an oxidation procedure involving Na2Cr2O7 it was possible to transform chlorite to a vermiculite having similar X‐ray diffraction properties to soil vermiculite. The transformation was demonstrated on intact clay‐sized fractions of a Silurian mudstone and on chlorite separated electromagnetically from a soil derived from Lower Palaeozoic sediments.