Dark brown, almost black crystals of the rare vanadium mineral bokite from one of the few localities known worldwide: Monument No2 Mine, Apache County, Arizona, United States of America. — Photo: David Hospital · CC BY-SA 4.0
Bokite
Bokite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula (Al,Fe)₁.₃(V⁵⁺,V⁴⁺,Fe³⁺)₈O₂₀·7.5H₂O.
It crystallizes in the monoclinic crystal system (space group C2/m). It is a member of the Straczekite structural group.
Key properties: Mohs hardness 3; specific gravity 2.97–3.1; Black, may be brownish black streak; Semimetallic to dull luster; optically biaxial.
IMA symbol Bkt, IMA status: approved, named in 1963.
Found in carbonaceous vanadiferous shales (Kurumsak area, Kazakhstan); in rich U–V ore in Triassic stream channels and impregnating sandstone (Monument No. 2 mine, Arizona, USA).
It is found associated with Jarosite, kazakhstanite (Kurumsak area, Kazakhstan); navajoite (Monument No. 2 mine, Arizona, USA).
The name refers to Ivan Ivanovich Bok (1898–1983), Kazakh geologist, Institute of Geosciences, Alma-Ata, Kazakhstan.