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Curite is a rare mineral with the chemical composition Pb3[(UO2)4|O4|(OH)3]2·2 H2O.[1] It is therefore a hydrated lead uranyl oxide, which forms red needles or orange, massive aggregates.
| Curite | |
|---|---|
| |
| General | |
| Category | Oxide mineral |
| Formula (repeating unit) | Pb3[(UO2)4|O4|(OH)3]2·2 H2O[1] |
| IMA symbol | Cui[2] |
| Strunz classification | 4.GB.55 |
| Crystal system | Orthorhombic |
| Crystal class | orthorhombic-dipyramidal; 2/m 2/m 2/m[3] |
| Space group | Pnam[4] |
| Unit cell | a = 12.551 Å, b = 13.02 Å, c = 8.40 Å; Z = 2 |
| Identification | |
| Color | red, reddish orange, brownish yellow. |
| Crystal habit | needles, acicular, massive, compact earthy. |
| Cleavage | {100}, imperfect}[5] |
| Fracture | uneven |
| Tenacity | brittle |
| Mohs scale hardness | 4-5 |
| Luster | adamantine |
| Streak | orange |
| Diaphaneity | transparent |
| Density | measured: 6.98–7.4; calculated: 7,37[5] |
| Optical properties | biaxial (-) |
| Refractive index | nα = 2.060 nβ = 2.110 nγ = 2.150[6] |
| Birefringence | 0.090 |
| Pleochroism | Visible: X = b = pale yellow, Y = a = light red-orange, Z = c = dark red-orange |
| 2V angle | 70° (measured); 80° (calculated)[6] |
| Other characteristics |  Radioactive |
Curite was first found at Shinkolobwe mine (formerly known as "Kasolo mine“) in Katanga Province in the Democratic Republic of the Congo. Alfred Schoep (1881–1966) described the mineral for the first time in 1921 and named it after physicist and Nobel laureate Pierre Curie (1859–1906).[7]
The mineral is classified according to Strunz as part of the uranyl hydroxides, forming its own group with additional cations (K, Ca, Ba, Pb etc.) and primarily UO2(O,OH)5 pentagonal polyhedra with system number 4.GB.55.
Dana classifies the mineral to the oxides and hydroxide, as part of the uranium- and thorium-containing oxides with oxidation state 6+ containing Pb, Bi, hydroxyl groups or water.
Curite crystallises orthorhombically in space group Pnam with the lattice parameters a = 12,56 Å; b = 13,02 Å und c = 8,40 Å[4] and two formula units per unit cell.[3]
The crystal structure consists of layers of corner- and edge-sharing uranyl polyhedra, in which the uranyl cation shows both pentagonal-bipyramidal and square-bipyramidal coordination. The lead cations connect these layers by coordinating to the oxygen atoms of uranyl group.[8]
The mineral is radioactive because of its uranium content of about 63%. Considering the composition with respect to the ideal sum formula, a specific activity of about 113,4 kBq/g[3] can be given. The absolute value of any given mineralogical sample may vary drastically depending on the general composition of the mineral with its matrix, the amount of material and its age.
Curite is a secondary uranium mineral, which forms by alteration of geologically old uraninite. Additionally, lead atoms form due to radioactive decay.[8] Curite is found in the oxidation zone along with dewindtite, fourmarierite, kasolite, rutherfordine, schoepite, soddyite, sklodowskite, torbernite und vandendriesscheite.
Curit has been found, apart from its type locality Shinkolobwe mine, at a further 50 localities, e.g. in Egypt; Northern Territory, Australia; Baden-Württemberg, Bayern, Rhineland-Palatinate and Saxony, Deutschland; Auvergne, Bretagne, Alsace und Limousin, France; Lombardy and Trentino-Alto Adige/Südtirol, Italy; Northwest Territories, Canada; Fianarantsoa, Madagascar; Aust-Agder and Telemark, Norway; Karelia, Russia; Namaqualand, South Africa; Bohemia and Moravia, Czechia; Baranya and Heves, Hungary as well as in Colorado, New Hampshire und New Mexico, USA.[9]
Because of its radioactivity samples of this mineral should be kept in air-tight containers. Inhaling the dust or incorporation should be avoided.
