Halloysite water content

Halloysite has a chemical composition similar to kaolinite, but with a higher water content. The layers of halloysite are like those in kaolinite, but they are stacked with highly random displacements parallel to the layers, as opposed to the regular stacking found in kaolinite. The interlayer distance is greater in halloysite, allowing for the presence of a sheet of water molecules. A small ion-exchange capacity is measurable in kaolinite and halloysite minerals, which arises from a small amount of iso-morphous replacement of Si4+ or Al3+ in the framework 234). 

Halloysite has the same stoichiometrical composition of kaolinite, except for its water content. Layered halloysite occurs mainly in two different polymorphs, the hydrated form (with interlayer spacing of 10 A) with the formula Al2Si20s(0H)4.2H20 and the anhydrous form (with interlayer spacing of 7 A) and kaolinite composition - Al2Si20 (0H)4. The intercalated water is weakly bound and can be readily and irreversibly removed 0oussein et at, 2005). 

The interlayer water in halloysite is easily removed dining drying, and this dehydration is irreversible. Because of this phenomenon, soil engineering tests on air-dried samples can give different results than those performed on samples at the original field moisture content. For this reason, it is especially important that laboratory tests on soils with appreciable halloysite content be carried out on samples at the original field moisture content (Holtz and Kovacs, 1981 Hilf, 1975). 

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