kaolinite - teaching hand/display specimen of the primary constituent of kaolin clay
Kaolinite is the primary constituent of kaolin clay. Its physical structure is like a sandwich, with aluminum hydroxide layers, called gibbsite layers, bonded to silicate sheets. These sheets are electrically neutral, so they are bonded by very weak van de Waals forces, easily sliding apart to give kaolinite its softness and greasy feel.
Rocks with a silica-rich composition that contain aluminosilicate minerals weather to clays. This kaolinite was formed by the hydrothermal alteration of tuffs, welded volcanic ash with a composition similar to that of granite. Granitic rocks, since they contain abundant feldspar, are a common source for kaolinite.
Kandites are a group of clays with a sheet structure similar to that of kaolinite. Anauxite, dickite and nacrite are other kandites. Halloysite is similar, but with water molecules between the sheets. Because kaolinite does not absorb water, it does not expand when it comes in contact with water and is the preferred type of clay for the ceramics industry.
This kaolinite comes from the inactive Huntley Kaolinite Mine in Mono County, California.
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