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Friday, January 14, 2011


Weathering debris
Weathering acts upon rocks to produce solid, colloidal, and soluble materials. These materials differ in size and behaviour (Gerrard, 2007):

1 Solids range from boulders, through sand, and silt, to clay (Table 3.1). They are large, medium, and small fragments of rock subjected to disintegration and decomposition plus new materials, especially secondary clays built from the weathering products by a process called neoformation. At the lower end of the size range they grade into pre-colloids, colloids, and solutes.

2 Solutes are ‘particles’ less than 1 nm (nanometre) in diameter that are highly dispersed and exist in molecular solution. 

3 Colloids are particles of organic and mineral substances that range in size from 1 to 100 nm. They normally exist in a highly dispersed state but may adopt a semi-solid form. Common colloids produced by weathering are oxides and hydroxides of silicon, aluminium, and iron. Amorphous silica and opaline silica are colloidal forms of silicon dioxide. Gibbsite and boehmite are aluminium hydroxides. Hematite is an iron oxide and goethite a hydrous iron oxide. Pre-colloidal materials are transitional to solids and range in size from about 100 to 1,000 nm.

Sources : Gerrard, John.2007.FUNDAMENTALS OF GEOMORPHOLOGY. New York : Routledge 270 Madison Avenue

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