AN INTERSTRATIF IED ILL ITE-SMECTITE FROM DENCHWORTH SERIES SOIL IN WEATHERED OXFORD CLAY

in weathered Oxford Clay has been investigated in detail. It contains a layer silicate mineral, almost free from impurities, that is a randomly interstratified mixture of approximately 45 % expanding and 55 % non-expanding i terlayers with the following unit formula: Na0.33K0.29(All.41Fe0.34Mg0.26)(Si3.60AI0.40)Oll. Computer-simulated iffraction patterns howed that experimental patterns are best matched when an average diffracting packet consists of between 4 and 5 2: 1 layer silicate units. Correction of the chemical composition for external exchangeable ions associated with such small packets gives non-expanding interlayers a charge density of 0'69K/Si4Oll and expanding interlayers one of 0"57M~/Si4011. The relationship between these values and those of mica and regularly expanding minerals is briefly discussed