Tangeite

(repeating unit)CaCu(VO₄)(OH)IMA symbolTg^[1]Strunz classification8.BH.35Dana classification41.05.01.06Crystal systemOrthorhombicCrystal classDisphenoidal (222)
H-M symbol: (2 2 2)Space groupP2₁2₁2₁Unit cella = 7.45 Å, b = 9.26 Å
c = 5.91 Å; Z = 4IdentificationColorYellow, yellow-green, olive green, green to dark greenCrystal habitRarely as short prismatic crystals, commonly as fibrous to botryoidal encrustationsCleavagePerfect on {010}, good on {001}TenacityBrittleMohs scale hardness3.5LusterVitreous, pearly on cleavage facesStreakLight yellow greenDiaphaneityTransparent, TranslucentSpecific gravity3.75 - 3.84Optical propertiesBiaxial (-)Refractive indexn_α = 2.010 n_β = 2.050 n_γ = 2.090Birefringence0.082V angle83° (measured)References^[2][3][4]

Tangeite, also known as calciovolborthite, is a calcium, copper vanadate mineral with formula: CaCu(VO₄)(OH). It occurs as a secondary mineral that can be found in sandstone and also in the oxidized zones of vanadium bearing deposits.

It was named in 1925 by Aleksandr Evgenievich Fersman for its discovery locality in the Tange Gorge, Ferghana Valley, Alai Mountains, Kyrgyzstan.^[2]