- Mottramite
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Mottramite General Category Vanadate minerals Chemical formula 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).
References
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