Stracherite, BaCa6(SiO4)2[(PO4)(CO3)]F, the first CO3-bearing intercalated hexagonal antiperovskite from Negev Desert, Israel

Abstract

The new mineral stracherite, BaCa6(SiO4)2[(PO4)(CO3)]F [R3m, a = 7.0877(5), c = 25.201(2), V = 1096.4(1)3, Z = 3], belongs to the zadovite group, which also includes zadovite, BaCa6[(SiO4)(PO4)](PO4)2F; aradite, BaCa6[(SiO4)(VO4)](VO4)2F; and gazeevite, BaCa6(SiO4)2(SO4)2O. All minerals of this group exhibit single-layer antiperovskite modules, which are intercalated with tetrahedral layers. In stracherite, the first CO3-bearing intercalated hexagonal antiperovskite, about 38% of the (PO4)3- tetrahedra are randomly substituted by planar (CO3)2- groups. The mineral was discovered in spurrite rocks of the Hatrurim Complex in the Negev Desert near Arad, Israel. Associated minerals are spurrite, calcite, brownmillerite, shulamitite, CO3-bearing fluorapatite, fluormayenite-fluorkyuygenite, and ariegilatite. The empirical formula of stracherite is: (Ba0.96K0.02Na0.01)S0.99Ca6.01[(SiO4)1.86 (PO4)0.12(AlO4)0.01(TiO4)0.01]S2[(PO4)1.05(CO3)0.75(SO4)0.18(VO4)0.02]S2(F0.95O0.03)S0.98. Poikilitic crystals of stracherite are up to 0.5 mm in size and are confined to re-crystallization zones of spurrite marbles under the influence of by-products (gases, fluids) of combustion metamorphism..