The First Find of Mannardite in Russia

Abstract

Mannardite was found in a type of Cr–V–bearing metamorphic rock of the Slyudyanka complex (South Baikal region). The X-ray data of the mineral are recalculated for three scenarios taking into account possible variations of the mannardite structure. The mean chemical composition is as follows (14 analyses, wt %): 0.11 SiO₂, 52.08 TiO₂, 6.19 VO₂, 13.51 V₂O₃, 5.50 Cr₂O₃, 0.24 Al₂O₃, 0.16 Fe₂O₃, 0.05 MgO, 20.09 BaO, 2.09 H₂O (the H₂O, VO₂, and V₂O₃ contents are recalculated). The formula of the mean composition is (Ba_1.06H₂O_0.94)(Ti_5.27Si_0.21V_0.61⁴⁺V_1.453+Cr_0.59Fe_0.02Mg_0.01)O₁₆. Mannardite is characterized by the presence of different valent V. The mineral can be hydrous with molecular H₂O or hydroxylion in tunnels or anhydrous. Mannardite can be considered an indicator of the hydroxyl or oxygen regime of petrogenetic processes.