Kyzylkumite, Ti (sub 2) V (super 3+) O (sub 5) (OH); new structure type, modularity and revised formula

The crystal structure of kyzylkumite, ideally Ti (sub 2) V (super 3+) O (sub 5) (OH), from the Sludyanka complex in South Baikal, Russia was solved and refined (including the hydrogen atom position) to an agreement index, R (sub 1) , of 2.34% using X-ray diffraction data collected on a twinned crystal. Kyzylkumite crystallizes in space group P2 (sub 1) /c, with a=8.4787(1), b=4.5624(1), c=10.0330(1) Aa, beta =93.174(1) degrees , V=387.51(1) Aa (super 3) and Z=4. Tivanite, TiV (super 3+) O (sub 3) OH, and kyzylkumite have modular structures based on hexagonal close packing of oxygen, which are made up of rutile [TiO (sub 2) ] and montroseite [V (super 3+) O(OH)] slices. In tivanite the rutile:montroseite ratio is 1:1, in kyzylkumite the ratio is 2:1. The montroseite module may be replaced by the isotypic paramontroseite V (super 4+) O (sub 2) module, which produces a phase with the formula Ti (sub 2) V (super 4+) O (sub 6) . In the metamorphic rocks of the Sludyanka complex, vanadium can be present as V (super 4+) and V (super 3+) within the same mineral (e.g. in batisivite, schreyerite and berdesinskiite). Kyzylkumite has a flexible composition with respect to the M (super 4+) /M (super 3+) ratio. The relationship between kyzylkumite and a closely related Be-bearing kyzylkumite-like mineral with an orthorhombic norbergite-type structure from Byrud mine, Norway is discussed. Both minerals have similar X-ray powder diffraction patterns.