Original paper
Schiavinatoite, (Nb,Ta)BO4, the Nb analogue of behierite
Demartin, Francesco; Diella, Valeria; Gramaccioli, Carlo M.; Pezzotta, Federico
European Journal of Mineralogy Volume 13 Number 1 (2001), p. 159 - 165
published: Jan 31, 2001
Abstract
The new mineral schiavinatoite (Nb,Ta)BO4, the niobium analogue of behierite, has been found in a boronrich pegmatite at Antsongombato, south of Betafo, in the Malagasy Republic, as portions of a greyish-pink bipyramidal crystal of Nb-rich behierite. Associated minerals are rhodizite, liddicoatite, spodumene, pollucite, danburite, apatite. The mineral is tetragonal, space group I41/amd, isostructural with behierite (zircon-type), with a = 6.219(5), c = 5.487(5) Å, V = 212.2(5) Å3, Z = 4, Dcalc = 6.548 g/cm3. The strongest lines in the X-ray powder diffraction pattern [d in Å (I, hkl)] are: 4.115(100,101), 3.110(84,200), 2.328(49,112), 1.598(42,312), 2.481(36, 211), 1.939(29,301), 1.646(25,321). Mohs's hardness is 8. Luster is vitreous, transparent in thin section, streak is white, the crystal is uniaxial (+) with average n = 2.30(5). The structure has been refined from single-crystal data, using 178 observed unique reflections to R = 0.011, Rw = 0.014.
Keywords
schiavinatoite • new mineral • behierite • niobium • tantalum • borate • crystal structure • chemical composition