English: Autunite from Luzy, France. (Robert Lauf collection)

A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are over 5400 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates.

The phosphate minerals have one or more phosphate anions (PO4-3).

Autunite is a scarce hydrous calcium uranyl phosphate mineral, Ca(UO2)2(PO4)2·11H2O. It has a nonmetallic luster, a yellowish to greenish color, a pale yellow streak, is fairly soft (H = 2 to 2.5 on the Mohs Hardness Scale), and is radioactive. Autunite is a secondary uranium mineral that forms by alteration of uraninite (or other primary U minerals) in an oxidizing environment. The original U+4 ions in uraninite get oxidized into U+6 and usually become incorporated into uranyl ions, (UO2)+2. In the presence of water, calcium, and phosphorus, autunite can form.

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Photo gallery of autunite:

www.mindat.org/gallery.php?min=433