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 (barite) and strontium (celestite) 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 colour 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. Anhydrite is commonly associated with calcite, halite, and sulfides such as galena, chalcopyrite, molybdenite, and pyrite in vein deposits. This article is about minerals in the geologic sense; for nutrient minerals see dietary mineral; for the band see Mineral (band). ... A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Atomic mass 40. ... Sulfate is the IUPAC name for the SO42- ion, consisting of a central sulfur atom single bonded to four tetrahedrally oriented oxygen atoms. ... In mineralogy, shape and size give rise to descriptive terms applied to the typical appearance, or habit of crystals. ... Rose des Sables (Sand Rose), a formation of gypse crystal In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... In crystallography, the orthorhombic crystal system is one of the 7 lattice point groups. ... Cleaveage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types: Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes. ... A fracture is the separation of a body into two, or more, pieces under the action of stress. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... The refractive index of a material is the factor by which electromagnetic radiation is slowed down (relative to vacuum) when it travels inside the material. ... Pleochroism is an optical phenomenon where due to double refraction of light by a colored gem or crystal, the light is divided into two paths which are polarized at a 90° angle to each other. ... In any mineral, its streak refers to the color of its powder. ... Relative density (also known as specific gravity) is a measure of the density of a material. ... Fusibility is the ease with which a material will melt. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Atomic mass 40. ... Sulfate is the IUPAC name for the SO42- ion, consisting of a central sulfur atom single bonded to four tetrahedrally oriented oxygen atoms. ... In crystallography, the orthorhombic crystal system is one of the 7 lattice point groups. ... Symmetry is a characteristic of geometrical shapes, equations, and other objects; we say that such an object is symmetric with respect to a given operation if this operation, when applied to the object, does not appear to change it. ... Barium is also the Latin name for the city Bari in Italy. ... Baryte with Cerussite from Morocco Baryte with Galena and Hematite from Poland Barite (BaSO4) is a mineral consisting of barium sulfate. ... General Name, Symbol, Number strontium, Sr, 38 Chemical series alkaline earth metals Group, Period, Block 2, 5, s Appearance silvery white metallic Atomic mass 87. ... Celestite (SrSO4) is a mineral consisting of strontium sulfate. ... Quartz crystal A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. Chemical structure Gypsum from New South Wales, Australia Heating gypsum above approximately 150°C (302°F) partially dehydrates the mineral by driving off exactly 75% of the water contained in its chemical structure. ... Calcite from Brushy Creek Mine, Missouri, USA. The mineral calcite is a calcium carbonate corresponding to the formula CaCO3 and is one of the most widely distributed minerals on the Earths surface. ... Halite is the mineral of sodium chloride, NaCl, commonly known as rock salt. ... In chemistry, a sulfide (sulphide in British and Canadian English) is a chemical compound or combination of sulfur with an oxidation number of -2, with another chemical element or a radical thereof. ... Galena is a lead ore. ... Chalcopyrite is a copper iron sulfide mineral that crystallizes in the tetragonal system. ... Molybdenite is a mineral of molybdenum disulfide, MoS2. ... The mineral pyrite, or iron pyrite, is iron disulfide, FeS2. ...

Anhydrite is most frequently found in salt deposits with gypsum; it was, for instance, first discovered, in 1794, in a salt mine near Hall in Tirol. In this occurrence depth is critical since nearer the surface anhydrite has been altered to gypsum by absorption of circulating ground water. In chemistry, salt is a general term used for ionic compounds composed of positively charged cations and negatively charged anions, so that the product is neutral and without a net charge. ...

From an aqueous solution calcium sulfate is deposited as crystals of gypsum, but when the solution contains an excess of sodium or potassium chloride anhydrite is deposited. This is one of the several methods by which the mineral has been prepared artificially, and is identical with its mode of origin in nature, the mineral is common in salt basins. Dissolving table salt in water In chemistry, a solution is a homogeneous mixture of one or more substances (the solutes) dissolved in another substance (the solvent). ... General Name, Symbol, Number sodium, Na, 11 Series alkali metal Group, Period, Block 1 (IA), 3, s Density, Hardness 968 kg/m3, 0. ... General Name, Symbol, Number potassium, K, 19 Series alkali metals Group, Period, Block 1(IA), 4, s Density, Hardness 856 kg/m3, 0. ... The chloride ion is formed when the element chlorine picks up one electron to form the anion (negatively charged ion) Cl−. The salts of hydrochloric acid HCl contain chloride ions and are also called chlorides. ... For the term related to television programmes, see watershed (television). ...

The name anhydrite was given by A. G. Werner in 1804, because of the absence of water of crystallization, as contrasted with the presence of water in gypsum. Some other names for the species are muriacite and karstenite; the former, an earlier name, being given under the impression that the substance was a chloride (muriate). A peculiar variety occurring as contorted concretionary masses is known as tripe-stone, and a scaly granular variety, from Vulpino, near Bergamo, in Lombardy, as vulpinite; the latter is cut and polished for ornamental purposes. 1804 was a leap year starting on Sunday (see link for calendar). ... Bergamo is a town in Italy, in Lombardy, about 40km northeast of Milan. ... Lombardy (in Italian Lombardia) is a region in northern Italy between the Alps and the Po Valley. ...

References

• Dana's Manual of Mineralogy ISBN 0471032883
• Spencer, Leonard James. Anhydrite. 1911 Encyclopædia Britannica
• Th Mineralgalleries.com
• Webmineral
• Mindat.org
• Minerals.net