Schiavinatoite is a very rare

borate mineral The Borate Minerals are minerals which contain a borate anion group. The borate (BO3) units may be polymerised similar to the SiO4 unit of the silicate mineral class. This results in B2O5, B3O6, B2O4 anions as well as more complex structures whic ...

, and the

niobium Niobium is a chemical element; it has chemical symbol, symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and Ductility, ductile transition metal. Pure niobium has a Mohs scale of mineral hardness, Mohs h ...

endmember of a solid solution formed with béhierite.Demartin, F., Diella, V., Gramaccioli, C.M., and Pezzotta, F., 2001. Schiavinatoite, , the Nb analogue of behierite. European Journal of Mineralogy 13, 159-165 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 ''I''4₁/''amd'') and occur in

pegmatites A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic com ...

. Schiavinatoite and nioboholtite are minerals with essential

and

boron Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three ...

Occurrence and association

Schiavinatoite was detected in miaroles of a pegmatite at Antsongombato, Madagascar. It coexists with an

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of Hydroxide, OH−, Fluoride, F− and Chloride, Cl− ion, respectively, in the crystal. The formula of the admixture of ...

-group mineral, béhierite,

danburite Danburite is a calcium boron silicate mineral with a chemical formula of CaB2(SiO4)2. It has a Mohs hardness of 7 to 7.5 and a specific gravity of 3.0. The mineral has an orthorhombic crystal form. It is usually colourless, like quartz, but can ...

elbaite Elbaite, a sodium, lithium, aluminium boro-silicate, with the chemical composition Na(Li1.5Al1.5)Al6Si6O18(BO3)3(OH)4, is a mineral species belonging to the six-member ring cyclosilicate tourmaline group. Elbaite forms three series, with drav ...

– liddicoatite,

feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...

pollucite Pollucite is a zeolite mineral with the formula with iron, calcium, rubidium and potassium as common substituting elements. It is important as a significant ore of caesium and sometimes rubidium. It forms a solid solution series with analcime. I ...

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

, rhodizite, and

spodumene Spodumene is a pyroxene mineral consisting of lithium aluminium inosilicate, Li Al( Si O3)2, and is a commercially important source of lithium. It occurs as colorless to yellowish, purplish, or lilac kunzite (see below), or alternatively yellow ...

Crystal structure

The main facts about schiavinatoite's structure: * isostructural with

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of th ...

coordination number of 8 (coordination polyhedron is distorted triangular

dodecahedron In geometry, a dodecahedron (; ) or duodecahedron is any polyhedron with twelve flat faces. The most familiar dodecahedron is the regular dodecahedron with regular pentagons as faces, which is a Platonic solid. There are also three Kepler–Po ...

) * tetrahedrally-coordinated

* chains of edge-sharing BO₄ and NbO₈ polyhedra, parallel to 01* edge-sharing dodecahedra link the chains

References

Borate minerals Niobium minerals Tetragonal minerals Minerals in space group 141 {{mineral-stub