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Category Uranyl neso- and polysilicates
(repeating unit)
Strunz classification 9.AK.15
Crystal system Monoclinic
Crystal class Sphenoidal (2)
Unit cell a = 15.85 Å, b = 6.98 Å
c = 6.64 Å; β = 97.45°; Z = 2
Formula mass 586.36 g/mol
Color Light yellow, lemon-yellow, honey-yellow, straw-yellow, green-yellow
Crystal habit Crystals occur as stellate needle aggregates; as fibrous crusts, and massive
Crystal symmetry Monoclinic
H-M symbol: (2)
Space group: P21
Cleavage {100} Perfect
Fracture Uneven
Tenacity Brittle
Mohs scale hardness 2.5
Luster Vitreous to pearly; waxy or dull when massive
Streak Yellowish white
Diaphaneity Translucent to subtranslucent
Specific gravity 3.81 - 3.90
Optical properties Biaxial (-)
Refractive index nα = 1.643 nβ = 1.666 nγ = 1.669
Birefringence δ = 0.026
Pleochroism Weak; X = colorless; Y = pale canary-yellow; Z = canary-yellow
2V angle 32° to 45°, measured
Ultraviolet fluorescence Weak yellow-green under both short and long UV
Other characteristics Radioactive
References [1][2][3]

Uranophane Ca(UO2)2(SiO3OH)2·5H2O is a rare calcium uranium silicate hydrate mineral that forms from the oxidation of uranium bearing minerals. Uranophane is also known as uranotile. It has a yellow color and is radioactive.