Nb-containing titanite: new data and crystal structure refinement
Brigatti, M.F.; Caprilli, E.; Mottana, A.; Poppi, L.
published: Mar 5, 2004
Nb-containing titanite, Si1.000 (Ti0.748Al0.095Zr0.045 Nb0.041Ta0.001 Fe3+0.067Sn0.002Sb0.001)1.000(Ca0.986Ce0.004La0.001Mn0.004Na0.005 K0.001)1.001F0.055(OH)0.065O4.880, from San Vito quarry, Mt. Somma, Naples, Italy, is characterised by extensive substitutions in the six- and seven-fold coordination sites. Single-crystal X-ray diffraction study indicates this niobian titanite to be monoclinic (a = 6.557(1), b = 8.701(1), c = 7.077(1)Å, β = 113.86°) with C2/c symmetry. Crystal structure refinement (agreement factor, R = 0.027) suggests that the substitution mechanism (Al, Fe)3+ + (Nb, Ta)5+ = 2Ti4+ is primarily responsible for the incorporation of pentavalent metal ions in the octahedral site.