Schiavinatoite is a very rare mineral,
a natural
niobium
Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it has sim ...
borate with the chemical formula .
[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 BO
3 group, which is more common among minerals. Schiavinatoite is one of the most simple niobium minerals. It forms a solid solution with its
tantalum-analogue, béhierite. Both minerals possess zircon-type structure (tetragonal, space group ''I''4
1/''amd'') and occur in
pegmatites.
Schiavinatoite and
nioboholtite are minerals with essential
niobium
Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it has sim ...
and
boron
Boron is a chemical element with the 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 th ...
.
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 OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common e ...
-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
Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it has sim ...
coordination number of 8 (coordination polyhedron is distorted triangular dodecahedron)
* tetrahedrally-coordinated boron
Boron is a chemical element with the 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 th ...
* chains of edge-sharing BO4 and NbO8 polyhedra, parallel to 01* edge-sharing dodecahedra link the chains
References
Borate minerals
Niobium minerals
Oxide minerals
Tetragonal minerals
Minerals in space group 141
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