Term used to describe two types of stone, one of gypsum and one of limestone. True alabaster is hydrated calcium sulphate, a finely fibrous form of gypsum. It occurs as nodular masses with a felted, fibrous microstructure, variably intermixed with streaks of red or green clay. Deposits of economic size accumulate as precipitated salts in evaporating saline lakes in arid areas. The variety satin spar occurs in vein-like form with the fibres in regular parallel arrangement, giving the mass a silk-like lustre. Alabaster is slightly soluble in water and therefore not suitable for outdoor works; it is very soft and readily cut and polished with the simplest tools. It provides an excellent surface for painting and gilding, without priming being necessary. The second type is the stone that was referred to as alabaster by Theophrastus and Herodotus and that is now known as calcite alabaster, onyx-marble, Egyptian alabaster, or Oriental alabaster. Onyx-marble is a stalagmitic limestone marked with patterns of swirling bands of cream and brown. It was an admired decorative stone in the Ancient Near East and the Mediterranean region.