Minerals with a palmierite-type structure. Part I. Mazorite Ba₃(PO₄)₂, a new mineral from the Hatrurim Complex in Israel

The new mineral mazorite, ideally Ba-3(PO4)(2), a P-analogue of gurimite Ba-3(VO4)(2), was discovered in rankinite paralava hosted by the massive gehlenite-bearing pyrometamorphic rocks of the Hatrurim Complex in Israel. It has also recently been discovered in xenolith samples from the Bellerberg volcano in Germany. Holotype mazorite usually forms colourless plate-like crystals up to 70-100 mu m in length but also occurs in small aggregates in association with other rare Ba-bearing minerals such as zadovite, celsian, hexacelsian, bennesherite, sanbornite, walstromite, fresnoite, gurimite, alforsite and barioferrite. The mineral is transparent, exhibits vitreous lustre and has a good cleavage on (001). Optically, mazorite is uniaxial (+), with omega = 1.760(3) and epsilon = 1.766(3) (lambda = 589 nm). The empirical formula of the holotype mazorite calculated on 8O is (Ba2.69K0.22Na0.04Ca0.02Sr0.01)S-2.98(P1.16V0.57S0.24Al0.04Si0.03)S2.04O8. Mazorite crystallises in space group R3m, with unit-cell parameters a = 5.6617(5) angstrom, c = 21.1696(17) angstrom, V = 587.68(9) angstrom(3) and Z = 3. Its crystal structure consists of BaO12,BaO10 and PO4 polyhedra, ordered along the c-axis in PO4-BaO10-BaO12-BaO10-PO4 columnar arrangement characteristic for palmierite-supergroup minerals. A tetrahedrally coordinated site is generally occupied by P5+ but can be partially substituted by V5+ and S6+. This substitution is shown in the Raman spectrum of mazorite, which reveals bands that can be assigned to the stretching and bending vibrations of (PO4)(3-), (VO (4))(3-) and (SO4)(2-) groups. The Raman spectra of mazorite from two localities (Hatrurim and Bellerberg) and spectra of minerals belonging to the mazorite Ba-3(PO4) 2 to gurimite Ba-3(VO4) (2) solid-solution series are presented. The gradual shift of the Raman bands, caused by cation substitutions, is well observed. The high V5+-> P5+ substitution is also observed for gurimite, for which the first X-ray structural data are also presented. Mazorite and other Ba-bearing minerals crystallised from a small portion of residual melt enriched in incompatible elements, such as Ba, V, P, U, S, Ti and Nb, at a temperature of similar to 1000 degrees C.