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.
| Tangeite |
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| General |
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| Category | Phosphate mineral |
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Formula
(repeating unit) | CaCu(VO4)(OH) |
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| Strunz classification | 8.BH.35 |
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| Dana classification | 41.05.01.06 |
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| Crystal system | Orthorhombic |
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| Crystal class | Disphenoidal (222)
H-M symbol: (2 2 2) |
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| Space group | P212121 |
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| Unit cell | a = 7.45 Å, b = 9.26 Å
c = 5.91 Å; Z = 4 |
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| Identification |
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| Color | Yellow, yellow-green, olive green, green to dark green |
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| Crystal habit | Rarely as short prismatic crystals, commonly as fibrous to botryoidal encrustations |
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| Cleavage | Perfect on {010}, good on {001} |
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| Tenacity | Brittle |
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| Mohs scale hardness | 3.5 |
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| Luster | Vitreous, pearly on cleavage faces |
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| Streak | Light yellow green |
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| Diaphaneity | Transparent, Translucent |
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| Specific gravity | 3.75 - 3.84 |
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| Optical properties | Biaxial (-) |
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| Refractive index | nα = 2.010 nβ = 2.050 nγ = 2.090 |
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| Birefringence | 0.08 |
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| 2V angle | 83° (measured) |
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| References | [1][2][3] |
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It was named in 1925 by Aleksandr Evgenievich Fersman for its discovery locality in the Tange Gorge, Ferghana Valley, Alai Mountains, Kyrgyzstan.