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(named after the city of Autun, in Saône-et-Loire Department France), a mineral of the uranite group. Autunite has a chemical formula of Ca(UO2)2[PO4]2·8H2O; it contains 62.7 percent UO3. The mineral crystallizes in the tetragonal system, primarily forming thin tabular, micaceous, or tetragonal crystals. Scaly aggregates also occur. Autunite varies in color from lemon yellow to sulfur yellow; sometimes it is green. The mineral has a pearly luster and is highly radioactive. Its hardness on Mohs’ scale is 2–2.5, and its density is 3,050–3,190 kg/m3. Autunite is formed as a result of surface changes in various uranium minerals (particularly uraninite), in hydrothermal veins, and in pegmatites. It is an ore of uranium.