Clarkeite is a uranium oxide mineral with the chemical formula(Na,Ca,Pb)
2
(UO
2
)
2
(O,OH)
3
or (Na,Ca,Pb)(UO
2
)O(OH)·0-1H
2
O
.

Clarkeite
General
CategoryMineral
Formula
(repeating unit)
(Na,Ca,Pb)
2
(UO
2
)
2
(O,OH)
3
or (Na,Ca,Pb)(UO
2
)O(OH)•0-1H
2
O
IMA symbolCke[1]
Strunz classification4.GC.05
Dana classification5.4.1.1
Crystal systemTrigonal
Space groupR3m (No. 166)
Unit cell239.11 Å3 (Calculated from unit cell)
Identification
ColourDark red-brown, dark brown
CleavageNone observed
FractureConchoidal, sub-conchoidal
Mohs scale hardness4–4.5
LusterResinous, waxy, greasy
StreakYellow-brown
DiaphaneityTranslucent
Specific gravity6.39
Density6.39 g/cm3 (Measured)
Birefringence0.111
PleochroismWeak
2V angleMeasured 30° to 50°, Calculated 32°
DispersionRelatively weak
Other characteristics Radioactive

Its color varies from dark brown to reddish orange. Clarkeite forms by oxidation and replacement of uraninite late during pegmatite crystallization. Although uraninite-bearing granite pegmatites are common, clarkeite is rare and occurs intimately intergrown with other uranium minerals.

It is known from only two localities; the Spruce Pine pegmatite district in western North Carolina, US, and Rajputana, in the Ajmer district, India. Clarkeite is the only known naturally occurring high-temperature uranate. The general formula for ideal clarkeite is Na[(UO
2
)O(OH)](H
2
O)
0–1
.

It was named for Frank Wigglesworth Clarke (1847–1931), American mineral chemist, and former chief chemist of the United States Geological Survey.

See also

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References

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  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.