Mottramite

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Mottramite
Mottramite.jpg
Mottramite (yellow) with fluorite and quartz. From Lower Silesia, Poland.
General
Category Vanadate minerals
Formula
(repeating unit)
PbCu(VO4)(OH)
Strunz classification 08.BH.40
Crystal symmetry mmm (2/m 2/m 2/m) - Dipyramidal
Unit cell a = 7.68Å, b = 9.27Å, c = 6.03Å
Identification
Color Grass-green, olive-green, yellow-green, siskin-green, blackish brown, nearly black
Crystal system Orthorhombic
Cleavage None observed
Fracture Irregular/uneven, sub-conchoidal
Tenacity Brittle
Mohs scale hardness 3 - 3½
Luster Greasy
Streak Yellowish green
Diaphaneity Transparent, opaque
Specific gravity 5.9
Optical properties Biaxial (-)
Refractive index nα = 2.170(2) nβ = 2.260(2) nγ = 2.320(2)
Birefringence δ = 0.150
Pleochroism Visible
2V angle Measured: 73° , Calculated: 46°
Dispersion strong r > v rarely r < v

Mottramite is an orthorhombic mineral, PbCu(VO4)(OH), at the copper end of the descloizite group. It was formerly called cuprodescloizite or psittacinite (this mineral characterized in 1868 by Frederick Augustus Genth).

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