Haidingerite is a calcium arsenate mineral with formula Ca(AsO3OH)·H2O. It crystallizes in the orthorhombic crystal system as short prismatic to equant crystals. It typically occurs as scaly, botryoidal or fibrous coatings. It is soft, Mohs hardness of 2 to 2.5, and has a specific gravity of 2.95. It has refractive indices of nα = 1.590, nβ = 1.602 and nγ = 1.638. It was originally discovered in 1827 in Jáchymov, Czech Republic. It was named to honor Austrian mineralogist Wilhelm Karl Ritter von Haidinger (1795–1871). It occurs as a dehydration product of pharmacolite in the Getchell Mine, Nevada. See also List of minerals named after people References Palache, C., H. Berman, and C. Frondel (1951) Dana’s system of mineralogy, (7th edition), v. II, pp.708–709. Calcium minerals Arsenate minerals Orthorhombic minerals Minerals in space group 60