Schiavinatoite

Schiavinatoite is a very rare borate mineral, and the niobium endmember of a solid solution formed with béhierite.

Schiavinatoite is classified as monoborate. It contains tetrahedral borate anion instead of planar BO₃ group, which is more common among minerals. Schiavinatoite is one of the most simple niobium minerals. Both minerals possess zircon-type structure (tetragonal, space group I4₁/amd) and occur in pegmatites. Schiavinatoite and nioboholtite are minerals with essential niobium and boron.

Occurrence and association

Schiavinatoite was detected in miaroles of a pegmatite at Antsongombato, Madagascar. It coexists with an apatite-group mineral, béhierite, danburite, elbaite–liddicoatite, feldspar, pollucite, quartz, rhodizite, and spodumene.

Crystal structure

The main facts about schiavinatoite's structure:

• isostructural with zircon
• niobium coordination number of 8 (coordination polyhedron is distorted triangular dodecahedron)
• tetrahedrally-coordinated boron
• chains of edge-sharing BO₄ and NbO₈ polyhedra, parallel to [001]
• edge-sharing dodecahedra link the chains

References