Chromium-rich vanadio-oxy-dravite from the Tzarevskoye uranium-vanadium deposit, Karelia, Russia: a second world-occurrence of Al-Cr-V-oxy-tourmaline.

A green tourmaline sample from the Tzarevskoye uranium-vanadium deposit, close to the Srednyaya Padma deposit, Lake Onega, Karelia Republic, Russia, has been found to be the second world-occurrence of Cr-rich vanadio-oxy-dravite in addition to the Pereval marble quarry, Sludyanka crystalline complex, Lake Baikal, Russia, type-locality. From the crystal-structure refinement and chemical analysis, the following empirical formula is proposed: X(Na0.96K0.02□0.02)Σ1.00 Y(V1.34Al0.68Mg0.93Cu0.022+Zn0.01Ti0.01)Σ3.00 Z(Al3.19Cr1.36V0.03Mg1.42)Σ6.00(TSi6O18)(BBO3)3V(OH)3 W[O0.60(OH)0.23F0.17]Σ1.00.Together with the data from the literature, a compositional overview of Al-V-Cr-Fe3+-tourmalines is provided by using [6]Al-V-Cr-Fe3+ diagrams for tourmaline classification. These diagrams further simplify the tourmaline nomenclature as they merge the chemical information over the octahedrally-coordinated sites (Y and Z) by removing the issues of uncertainty associated with cation order-disorder across Y and Z. Results show the direct identification of tourmalines by using the chemical data alone. [ABSTRACT FROM AUTHOR]