My periodic table poster is now available! Gypsum. Description from the source: Gypsum (Ca SO4x2 H2O mon.), desert of Morocco. Geminate crystals with sand inclusions. 3x2,7x1,2 cm; 6 g. Source: Simone Citon Contributor: John Gray Acquired: 10 January, 2009 Text Updated: 10 January, 2009 Price: Trade Size: 1.2" Composition: CaSO4.2H2O