Uranite

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Uranite

 

the name of a group of minerals that are aqueous phosphates and arsenates of uranyl, (UO2)2+. Uranites are characterized by a well-defined mica-like cleavage in one direction; the crystals are lamellar in form. The general formula for uranite is A(UO2)2(XO4)2 · nH2O, where A is H3O, Na, K, Ca, Ba, Cu, Mg, or some other element and X is P or As.

The uranite group includes about 30 mineral species, the primary minerals being torbernite and autunite. The crystal structure is based on layers consisting of discrete uranyl groups (UO2)2+ and phosphate or arsenate tetrahedrons [PO4]3– and [AsO4]3–; the A cations, coordinated by water molecules, are located between the layers. Uranites are subdivided according to the degree of hydration into primary forms, where n = 8 or more (the torbernite series), and meta-forms, where n = 8 or less (the metatorbernite series). The primary forms lose part of their water easily when becoming meta-forms.

The most common colors are yellow and green; uranites containing Co and Mn are pink. Uranites have a pearly luster, a hardness of 2–2.5 on Mohs’ scale, and a density of 3,200–3,600 kg/m3. Uranites that do not contain copper, iron, lead, cobalt, or manganese are distinguished by strong luminescence. They are radioactive and dissolve easily in acid. All the uranites are hyper-genic minerals and are especially typical of the oxidation zone of uranium-sulfide deposits. They are ores of uranium.

REFERENCE

Soboleva, M. V., and I. A. Pudovkina. Mineraly urana: Spravochnik. Moscow, 1957.

L. N. BELOVA