Tangeite

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

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