Ceramics
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FELDSPARS

Orthoilase - K2O . Al2O3 . 6SiO2

Albite - Na2O . Al2O3 . 6SiO2

Anorthite - CaO . Al2O3 . 2SiO2

Feldspar is disintegrated by geologic weathering, the alkali part, namely; soda, potash, or lime, being relatively soluble, is carried off by water. Leaving the alumina and silica, part of the silica is split off by chemical combination. The remaining alumina and silica after long exposure to moisture, then becomes hydrated, or chemically combined with water. This takes millions of years.

Plasticity - with proper amount of water, will tend to hold any shape which is given to it.

To some degree, plasticity can be attributed to fineness of grain. Each grain lubricated with water-surface with moisture, tend to make the particles cling to one another and thus, cause the entire mass to retain a given shape. The fact is that one can model with wet sand. The smaller the grain=better modeling. Also, chemical reaction between particles. Fineness of particle size: a grain of sand=1/500 inch Clay .7 microns in diameter (1 micron is 1/25,000 of an inch) A particle is a flat, shinglelike shape. Particles tend to slide together and give support to one another.