Anhydrite

Anhydrite is a mineral—anhydrous calcium sulfate, CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium (baryte) and strontium (celestine) sulfates, as might be expected from the chemical formulas. Distinctly developed crystals are somewhat rare, the mineral usually presenting the form of cleavage masses. The hardness is 3.5 and the specific gravity 2.9. The color is white, sometimes greyish, bluish, or purple. On the best developed of the three cleavages, the lustre is pearly; on other surfaces it is vitreous. When exposed to water, anhydrite readily transforms to the more commonly occurring gypsum, (CaSO4·2H2O) by the absorption of water. This transformation is reversible, with gypsum or calcium sulfate hemihydrate forming anhydrite by heating to ~200°C under normal atmospheric conditions. Anhydrite is commonly associated with calcite, halite, and sulfides such as galena, chalcopyrite, molybdenite, and pyrite in vein deposits.

Read more about AnhydriteOccurrence, Naming History

Other articles related to "anhydrite":

Salt Dome Caprock
... (salt) is removed first, leaving behind gypsum and anhydrite ... The anhydrite and gypsum react with organic material to form calcite ... classic Murray 1966 paper describes the generalized sequence as sediments-calcite-gypsum-anhydrite-salt ...
Salt Dome Gorleben - Underground Exploration
... The main objective of the underground exploration is the detection of rocksalts like top anhydrite which are required for the final storage ... Areas of missing top anhydrite and accompanying layers ... The top anhydrite is decomposed into individual plates ...
Staufen Im Breisgau - Geothermal Drilling Controversy
... The drilling perforated an anhydrite layer and caused high-pressure groundwater to come into contact with the anhydrite, which then began to expand ... "A geochemical process called anhydrite swelling has been confirmed as the cause of these uplifts ... This is a transformation of the mineral anhydrite (anhydrous calcium sulphate) into gypsum (hydrous calcium sulphate) ...
Calcium Sulfate - Dehydration Reactions
... °C are used in industrial calcination, but at these temperatures γ-anhydrite begins to form ... heating to 180 °C, the nearly water-free form, called γ-anhydrite (CaSO4·nH2O where n = 0 to 0.05) is produced ... γ-Anhydrite reacts slowly with water to return to the dihydrate state, a property exploited in some commercial desiccants ...