New minerals with a modular structure derived from hatrurite from the pyrometamorphic Hatrurim Complex. Part II. Zadovite, BaCa₆[(SiO₄)(PO₄)](PO₄)₂F and aradite, BaCa₆[(SiO₄)(VO₄)](VO₄)₂F, from paralavas of the Hatrurim Basin, Negev Desert, Israel

Zadovite, BaCa₆[(SiO₄)(PO₄)](PO₄)₂F (R3m, a = 7.0966(1) Å, c = 25.7284(3), V= 1122.13(3) ų, Z= 3) and aradite, BaCa₆[(SiO₄)(VO₄)] (VO₄)₂F(R3m,a = 7.1300(1),c = 26.2033(9) Å, V= 1153.63(6) A³,Z= 3) are two new mineral species of a novel modular structure type related closely to the structure of nabimusaite, KCa₁₂(SiO₄)₄(SO₄)₂O₂F Both minerals occur in paralavas enclosed in pyrometamorphic rocks of the Hatrurim Complex, Negev desert, Israel. Zadovite and aradite are colourless, transparent with a white streak, have a vitreous lustre and an uneven fracture. Both minerals are uniaxial (-) with refractive indices (589 nm) ω= 1.711(2), ε = 1.708(2) (zadovite) and ω = 1.784(3), ε = 1.780(3) (aradite). The zadovite structure type comprises two tetrahedral sites, which may host a broad compositional range of atoms such as Si, P, V and S. Results of electron microprobe analyses show a correlation between excess Si⁴⁺ and S⁶⁺ contents, suggesting the substitution scheme 2(P,V)⁵⁺ = Si⁴⁺ + S⁶⁺ at the tetrahedral sites. This points to the possibility of new minerals isostructural with zadovite with end-member formulae BaCa₆(SiO₄)₂[(PO₄)(SO₄)]F, BaCa₆(SiO₄)₂[(VO₄)(SO₄)]F, BaCa₆[(SiO₄)_1.5(SO₄)_0.5](PO₄)₂F and BaCa₆[(SiO₄)_1.5(SO₄)_0.5](VO₄)₂F. The Raman spectra of aradite and zadovite reflect the varying PO₄ (e.g. change of band intensity at ~ 1031 cm^-1) and VO₄ contents (e.g. change of band intensity at ~835 cm^-1). The presence of SO₄ leads to an additional Raman band at ~ 997 cm^-1. The structure of zadovite-series minerals belonging to the nabimusaite group is characterized by a 1 : 1 alternation of antiperovskite-like ([FCa₆](TO₄)₂}⁴⁺ modules and Ba(TO₄)⁴₂- modules.