Inclusions of Koragoite in Topaz from Pegmatites of the Mokrusha Deposit, Urals, Russia

The present communication is focused on inclusions in topaz from the Mokrusha pegmatite deposit, Urals. These inclusions are intergrown fine crystals of manganocolumbite, cassiterite and a mineral compositionally corresponding to niobium tungstate with minor Mn, Ta, and Fe. Electron microprobe and X-ray diffraction study has revealed that this mineral is identical to that previously described by A. V. Voloshin et al. (1997) in granite pegmatites of the Southwestern Pamir Mountains, Tajikistan. The crystal chemical formula of the mineral is (Mn2.02F0.98)Σ3.00(Nb2.296Ta0.640Ti0.062)Σ3.00(Nb1.04Mn0.960)Σ2.00(W1.343Nb0.664)Σ2.00O20.