Hydroxy interlayers in expansible layer silicates

Abstract--Vermiculites and smectites in soils and sediments are frequently partially interlayered or "chloritized". Dioctahedral expansible layer silicates are those most frequently interlayered, and hydroxy-Al appears to be the principal component ofthe non-exchangeable interlayer material. The most favorable soil conditions for interlayer formation appear to be: moderate pH (4.6-5.8), frequent wetting and drying cycles, and low organic matter content. In marine sediments, hydroxy-Mg interlayering may be significant. Soil-derived clays containing partially filled hydroxy-Al "brucite " sheets may be filled out with hydroxy-Mg. Under reducing conditions, hydroxy-Fe interlayers may be important. Depending on the OH/AI ratio and A1 content of hydroxy-Al interlayers, expansible ayer silicate may either promote or retard the formation of gibbsite. Interlayered xpansible ayer silicates also may be precursors to kaolinite