ABSTRACT
Illites in soils mainly originate from micas in the parent rocks. Vermiculites in soils form predominantly by the transformation of micas and also of chlorite. Kaolinite is the most ubiquitous secondary phyllosilicate in soils. Kaolinites in soils tend to be both smaller in particle size and also more irregular in shape than kaolinites from geological deposits such as the type kaolinites from either the state of Georgia in the United States or Cornwall in the United Kingdom. Kaolinites are usually the product of strong weathering and are therefore commonly formed in warm, humid climates and as a result of quite strong leaching. While commonly formed from volcanic materials, halloysite has been identified as a weathering product of a wide range of rock types, including granite, gneiss, dolerite, nephelinite, schist, greywacke, greenstone, granodiorite, gabbro, shale and amphibolite. Structural considerations also argue against the solid-state transformation of allophane to halloysite.
