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

Abstract

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 (Na 0.96 K 0.02 □ 0.02 ) Σ1.00 Y (V 1.34 Al 0.68 Mg 0.93 Cu 2+ 0.02 Zn 0.01 Ti 0.01 ) Σ3.00 Z (Al 3.19 Cr 1.36 V 0.03 Mg 1.42 ) Σ6.00 ( T Si 6 O 18 )( B BO 3 ) 3 V (OH) 3 W [O 0.60 (OH) 0.23 F 0.17 ] Σ1.00 . Together with the data from the literature, a compositional overview of Al–V–Cr–Fe 3+ -tourmalines is provided by using [6] Al–V–Cr–Fe 3+ 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.