The Collaborative International Dictionary
Volborthite
Volborthite \Vol"borth*ite\, n. [So named after Volborth, who first discovered it.] (Min.) A mineral occurring in small six-sided tabular crystals of a green or yellow color. It is a hydrous vanadate of copper and lime.
Wiktionary
volborthite
n. (context mineralogy English) A mineral containing copper and vanadium.
Wikipedia
Volborthite
Volborthite is a mineral containing copper and vanadium, with the formula Cu V O(O H)·2 HO. 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), CaCuVO(OH), is closely related.