Clays are earthy, fine grained rocks composed mainly of minerals of secondary origin - the clay minerals - among which the most predominant are the hy• drous aluminum silicates. The clay minerals, formed by the chemical weathering or alteration of aluminous minerals such as feldspar and mica, are…
Gypsum is a hydrous calciu~ sulphate (CaS04.2HiO), which, when calcined at temperatures ranging from 250° to 400°F, releases three quarters of its chemically • combined water. The resulting hemihydrate of calcium sulphate, commonly referred to as plaster of paris, when mixed with water, can be mo…