gypsum, calcium sulphate dihydrate, CaSO4 2H2O
location: donated from UA Little Rock

use in ceramics: calcium sulphate is the crystalline mineral from which plaster in made. It is not practical for glazes because its decomposition produces sulfur trioxide (SO3) which is dangerous to health and is destructive to the integrity of the glaze layer. Calcium sulphate is often found in raw clay deposits as a partially soluble impurity that causes efflorescence, the whitish or brownish dry or glassy scum left on the surface of a fired clay body.

use in paints: Gypsum, calcium sulfate dihydrate, can be used as an extender in paint and a filler in grounds.