Chromo-alumino-povondraite, NaCr3(Al4Mg2)(Si6O18)(BO3)3(OH)3O, is a new mineral of the tourmaline supergroup. It is found in metaquartzites of the Pereval marble quarry (Sludyanka, Lake Baikal, Russia) in association with dravite, oxy-chromium-dravite, oxy-dravite, quartz, calcite, chromphyllite, eskolaite, chromite, uvarovite, chromian phlogopite, and pyroxenes of the diopside-kosmochlor series, Cr-bearing tremolite, Cr-bearing titanite, Cr-bearing rutile, and pyrite.
The crystal structure of chromo-alumino-povondraite was refined to an R1 index of 1.68% using 1803 unique reflections collected with MoKα X-radiation. Ideally, chromo-alumino-povondraite is related to oxy-dravite and oxy-chromium-dravite by the homovalent substitution Cr3+ ↔ Al3+. Tourmaline with chemical compositions classified as chromo-alumino-povondraite can be either Al-dominant or Cr-dominant as a result of the compositional boundaries along the solid solution between Al and Cr3+ that are determined at Y+Z(Cr1.5Al5.5), corresponding to NaY(Cr1.5Al1.5)Z(Al4Mg2)Si6O18(BO3)3(OH)3O, and Y+Z(Cr5Al2), corresponding to NaY(Cr3)Z(Cr2Al2Mg2)Si6O18(BO3)3(OH)3O.