Chemistry:Clarkeite

Short description: Uranium oxide mineral

Clarkeite
General
Category	Mineral
Formula (repeating unit)	(Na,Ca,Pb)2(UO2)2(O,OH)3 or (Na,Ca,Pb)(UO2)O(OH)•0-1H2O
Strunz classification	4.GC.05
Dana classification	5.4.1.1
Crystal system	Trigonal
Space group	R3m (No. 166)
Unit cell	239.11 Å3 (Calculated from unit cell)
Identification
Colour	Dark red-brown, dark brown
Cleavage	None observed
Fracture	Conchoidal, sub-conchoidal
Mohs scale hardness	4–4.5
|re|er}}	Resinous, waxy, greasy
Streak	Yellow-brown
Diaphaneity	Translucent
Specific gravity	6.39
Density	6.39 g/cm3 (Measured)
Birefringence	0.111
Pleochroism	Weak
2V angle	Measured 30° to 50°, Calculated 32°
Dispersion	Relatively weak
Other characteristics	Radioactive

Clarkeite is a uranium oxide mineral with the chemical formula(Na,Ca,Pb)₂(UO₂)₂(O,OH)₃ or (Na,Ca,Pb)(UO₂)O(OH)·0-1H₂O.

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[(UO₂)O(OH)](H₂O)_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

• List of minerals
• List of minerals named after people
• Sodium uranate

References

• Clarkeite: New chemical and structural data
• Clarkeite: Clarkeite mineral information and data
• WebMineral