Volborthite

Volborthite is a mineral containing copper and vanadium, with the formula Cu₃V₂O₇(OH)₂·2H₂O. Found originally in 1838 in the Urals, it was first named knaufite but was later changed to volborthite for Alexander von Volborth (1800–1876), a Russian paleontologist.^[5]

Volborthite
Neon green crystals of volborthite are nestled in a vug in the matrix
General
Category	Polyvanadate minerals
Formula	Cu3V2O7(OH)2·2H2O
IMA symbol	Vbo[1]
Strunz classification	8.FD.05
Dana classification	40.03.10.01
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/m
Unit cell	a = 10.610(2) Å, b = 5.866(1) Å c = 7.208(1) Å; β = 95.04(2)°; Z = 2
Identification
Color	Olive-green, yellow-green; green to yellow-green in transmitted light
Crystal habit	Aggregates of scaly crystals, rosettes
Cleavage	Perfect
Mohs scale hardness	3+1⁄2
Luster	Vitreous, waxy, greasy, pearly
Streak	light green
Diaphaneity	Translucent
Specific gravity	3.5 - 3.8
Optical properties	Biaxial (+/-)
Refractive index	nα = 1.793 nβ = 1.801 nγ = 1.816
Birefringence	δ = 0.023
Pleochroism	Weak
2V angle	Measured: 63° to 83°
Dispersion	Translucent to Subtranslucent
Ultraviolet fluorescence	Non-fluorescent
Solubility	Soluble in acids
References	[2][3][4]

Tangeite (synonym: calciovolborthite), CaCuVO₄(OH), is closely related.

Occurrence

Volborthite was first described in 1837 for an occurrence in the Sofronovskii Mine, Yugovskii Zavod, Perm, Permskaya Oblast, Middle Urals, Russia.^[3]

It occurs as an uncommon oxidation mineral in vanadium bearing hydrothermal copper ores. It is associated with brochantite, malachite, atacamite, tangeite, chrysocolla, baryte and gypsum.^[2]