Brief Description: The term gypsum was known in the ancient times and included the mineral ?gypsum? and lime. It referred to the geode material that when baked and mixed with water turned hard and solid. For this reason, they used it in construction, mould making, fabrics, wine processing and painting. Furthermore, gypsum referred to alabaster, although the alabastrite stone was probably of calcite composition (Theophrastus). It has the chemical formula CaSO4?2H2O and belongs to the category Sulphuric Minerals. Its lustre is vitreous, pearly or silky. It can be colourless, white, grey and various shades of yellow, red and brown. Its is transparent to semitransparent. Its specific gravity is 4.5, its hardness 2 and its fusibility 3. It crystallizes in the monoclinic system and its crystals are tabular or prismatic, simple or often twin. The aggregates are schistose, grainy, fibrous, earthen, columnar, tree-like or rosette-like. The solid, fine-grained variety is called alabaster. It occurs in sedimentary rocks together with other evaporites, like alite, anhydrite, sylvine etc. 
Bibliography: Ευρετήριο ορυκτών ΑΠΘ στην ιστοσελίδα http://www.geo.auth.gr/106/az_gr.htm Τσιραμπίδης Α. Ο ορυκτός πλούτος της Ελλάδας. Εκδόσεις Γιαχούδη Θεσσαλονίκη, 2005, σελ. 391. Berry, L.G., Mason, B. and Dietrich, R.V. (1983). Mineralogy. W. H. Freeman and Company, San Francisco, 561 pp. Σαπουντζής, Η. και Χριστοφίδης, Γ. (1985). Ορυκτοδιαγνωστική. University Studio Press, Θεσσαλονίκη, 241 σ.