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Download hereGENERAL DESCRIPTION
Gypsum is an hydrated calcium sulphate. It rather frequently shows a twin that known as "swallowtail". It is of low temperature hydrothermal origins or is formed from brines evaporation within sediments.
The crystals are transparent, colourless to pale yellow, prismatic and frequently twinned. Several varieties are distinguished: the pink of sands or desert rose (this gypsum grew and imprisoned grains of sand); alabaster (it is a fine gypsum used for sculptures); selenite (which is an entirely transparent and colourless gypsum).
Some deposits: Winnipeg in Canada, the sulphur mines in Sicily, Naïca in the district of Chihuahua in Mexico (transparent crystals of more than 2 m length).
In France, one finds gypsum in abundance in the Paris basin (near Angervilliers in Essonne: white crystals of 10 cm); district of Sainte Marie aux Mines in Haut-Rhin; the mine of Tistoulet in Aude.
The place of conservation of the type of this species is unknown.
Did you know? Gypsum is used as a primary matierial for plaster manufacture
HISTORY : Name inspired from the Greek word "γυψοσ" [gupsos] and from the Latin "gypsum" meaning "plaster stone"
Species described in -315 by Theophrastus (372-287), Greek naturalist
Type-locality : unknown
CHEMICAL FORMULA : Ca SO4 2H2O
CRYSTAL SYSTEM : Monoclinic
COLOR : Colorless, white, yellow, blue, pink or reddish
DIAPHANIETY : Transparent to translucent
LUSTER : Sub-vitreous
STREAK : White
MORPHOLOGIE : Acicular to prismatic crystals, tabular, curved
HARDNESS : 1,5-2,0
CHEMICAL CLASS: 2,31
DENSITY : VI - Sulfates, chromates, tungstates and molybdates
GROUP : Gypsum-bassanite
STRUNZ CLASS BEFORE 2001 : 6/C.22-20
STRUNZ CLASS AFTER 2001 : 7.CD.30
