Autunite

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Autunite
AutuniteUSGOV.jpg
Autunite
General
Category Phosphate minerals
Formula
(repeating unit)
Ca(UO2)2(PO4)2·10-12H2O
Strunz classification 08.EB.05
Crystal symmetry Orthorhombic dipyramidal
H-M symbol: (2/m 2/m 2/m)
Space group: Pnma
Unit cell a = 14.0135(6) Å, b = 20.7121(8) Å, c = 6.9959(3) Å; Z=4
Identification
Formula mass 986.26
Color Lemon-yellow to sulfur-yellow, greenish yellow to pale green; may be dark green to greenish black
Crystal habit Tabular crystals, foliated or scaly aggregates, and in crusts
Crystal system Orthorhombic
Twinning Rare on {110}
Cleavage {001} perfect, {100} and {010} poor
Fracture uneven
Mohs scale hardness 2-2.5
Luster Vitreous - pearly
Streak Pale yellow
Diaphaneity Transparent to translucent
Specific gravity 3.1-3.2
Optical properties Biaxial (-)
Refractive index nα = 1.553 - 1.555 nβ = 1.575 nγ = 1.577 - 1.578
Birefringence δ = 0.003
Pleochroism X = colorless to pale yellow; Y = Z = yellow to dark yellow
2V angle Measured: 10° to 53°
Ultraviolet fluorescence Strong yellow-green fluorescence in UV; Radioactive
Solubility Soluble in acids
Alters to Dehydrates in air
Other characteristics Pseudotetragonal for synthetic material
References [1][2]

Autunite (hydrated calcium uranyl phosphate) with formula: Ca(UO2)2(PO4)2·10-12H2O is a yellow - greenish fluorescent mineral with a hardness of 2 - 2½. Autunite crystallizes in the orthorhombic system and often occurs as tabular square crystals. Due to the moderate uranium content of 48.27% it is radioactive and also used as uranium ore. If the mineral dries out, it converts to meta-autunite-I, which can turn into meta-autunite-II after heating. These two subsequent minerals are very rare in nature. For scientific studies it is recommended to store the mineral in a sealed container to minimize the water loss. Museums are known to have covered the mineral with lacquer to avoid drying of the mineral.

Autunite was discovered in 1852 near Autun, France. It occurs as an oxidation product of uranium minerals in granite pegmatites and hydrothermal deposits. Associate minerals include metaautunite, torbernite, phosphuranylite, saleeite, uranophane and sabugalite.[2]

Mining[edit]

Some autunite is found near Mount Spokane, Washington. 90,000 lbs of U3O8 were produced from nine properties, although most of the ore came from the Daybreak Mine.[3]

Gallery[edit]

References[edit]