Curite

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
Orange-red curite needles from Shinkolobwe mine, Katanga Province, Democratic Republic of the Congo
General
CategoryOxide mineral
Formula
(repeating unit)		Pb3[(UO2)4|O4|(OH)3]2·2 H2O[1]
IMA symbolCui[2]
Strunz classification4.GB.55
Crystal systemOrthorhombic
Crystal classorthorhombic-dipyramidal; 2/m 2/m 2/m[3]
Space groupPnam[4]
Unit cella = 12.551 Å, b = 13.02 Å,
c = 8.40 Å; Z = 2
Identification
Colorred, reddish orange, brownish yellow.
Crystal habitneedles, acicular, massive, compact earthy.
Cleavage{100}, imperfect}[5]
Fractureuneven
Tenacitybrittle
Mohs scale hardness4-5
Lusteradamantine
Streakorange
Diaphaneitytransparent
Densitymeasured: 6.98 - 7.4; calculated: 7,37[5]
Optical propertiesbiaxial (-)
Refractive indexnα = 2.060 nβ = 2.110 nγ = 2.150[6]
Birefringence0.090
PleochroismVisible: X = b = pale yellow, Y = a = light red-orange, Z = c = dark red-orange
2V angle70° (measured); 80° (calculated)[6]
Other characteristics Radioactive

Etymology and history

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]

Classification

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.

Crystal structure
Paragenesis of red curite with yellow schoepite, pseudomorphic after ianthinite on uraninite from Shinkolobwe, DRC

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]

Radioactivity

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.

Occurrence
Orange microcrystalline curite from Katanga Province, DRC.

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]

Precautions

Because of its radioactivity samples of this mineral should be kept in air-tight containers. Inhaling the dust or incorporation should be avoided.

Literature
  • Paul Ramdohr, Hugo Strunz (1978), Klockmanns Lehrbuch der Mineralogie (16. ed.), Ferdinand Enke Verlag, p. 560, ISBN 3-432-82986-8
  • Petr Korbel, Milan Novák (2002), Mineralien Enzyklopädie, Eggolsheim: Nebel Verlag GmbH, p. 111, ISBN 3-89555-076-0
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References
  1. Stefan Weiß (2008), Das große Lapis Mineralienverzeichnis. Alle Mineralien von A – Z und ihre Eigenschaften (5. vollkommen neu bearbeitete und ergänzte ed.), München: Weise, ISBN 978-3-921656-70-9
  2. L. N. Warr: IMA–CNMNC approved mineral symbols In: Mineralogical Magazine 2021, 85 291–320. DOI= 10.1180/mgm.2021.43 (PDF 320 kB)
  3. Webmineral Curite
  4. American Mineralogist Crystal Structure Database (AMCSD - Curite)
  5. Curite, In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Hrsg.): Handbook of Mineralogy, Mineralogical Society of America, 2001 (PDF 69 kB)
  6. Mindat Curite
  7. A. Schoep: La curite, nouveau minéral radioactif In: Comptes Rendus Hebdomadaires des Séances de l’Académie des Sciences 1921, 173, 1186–1187. (PDF (French) 91.6 kB)
  8. Y. Li, P. C. Burns: Investigations of crystal-chemical variability in lead uranyl oxide hydrates. I. CURITE, In: The Canadian Mineralogist 2000, Band 38, S. 727–735. (PDF 363.2 kB)
  9. Localities for curite Mineralienatlas and at Mindat
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