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clay - kaolin clay - teaching hand specimen of soft light tan kaolin

$ 7.50

kaolinite  Al2(Si2O5)(OH)4

Kaolinite is the primary constituent of kaolin clay and is one of the kaolin group of minerals. 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 usual softness and greasy feel. It has a similar structure to minerals in the serpentine group.  

Rocks with a silica-rich composition that contain aluminosilicate minerals weather to clays. This kaolinite was formed by the hydrothermal alteration of Pleistocene lacustrine sandstone and an underlying rhyolite. The sandstone was derived from granitic rocks, which contain abundant feldspar and after hydrothermal alteration or weathering are a common source for kaolinite.

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. It is also used as a filler in rubber and in paper, paint, plastics and cosmetics.

We have sold this clay as montmorillonite, an identification made by the California Division of Mines and Geology years ago. A recent analysis, by x-ray fluorescence spectroscopy, excellent for clays, has identified it as kaolin.

Potter Erik Ludwig created the two Southwestern pottery reproduction pieces shown using montmorillonite as a slip, but the behavior of the pigments on the slip made from this clay led him to believe that the clay was not montmorillonite, and we agree.

The specimens of this clay will stand up to student inspection, but will break if dropped. It is slightly light tan in color.

Select a specimen: When more than one specimen is shown, you can select a particular specimen by telling us what is in the photo with it, a black and silver pen, a black mechanical pencil or one of those plus some number of coins, or you can let us make the selection.

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