Volborthite

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
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

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.

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.

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.