Gorerite, CaAlFe11O19, a new mineral of the magnetoplumbite group from the Negev Desert, Israel

Abstract

AbstractGorerite, ideally CaAlFe11O19 is a new mineral and M-type hexaferrite of the magnetoplumbite group. It was found in ferrite-rich segregations of esseneite–gehlenite–wollastonite–anorthite melted rock of the ‘olive’ subunit of pyrometamorphic rocks located near Hatrurim Junction in the Negev Desert, Israel. Within these ferrite-rich segregations up to 100 μm in size, platy crystals of gorerite up to 50 μm in size intergrow with hibonite, hematite, maghemite, magnesioferrite, dorrite, barioferrite and andradite, forming aggregates. Additionally, small crystals of gorerite occur within magnesioferrite. Importantly, gorerite did not crystallise directly from the melt. Instead, it emerged through a reaction involving earlier crystallised hibonite and an iron-enriched melt, resulting in the partial or complete replacement of hibonite by gorerite. Gorerite appears grey in the reflected light (R = 18–23%), displaying distinct bireflectance: dark-grey perpendicular to Z and light-grey parallel to Z. Its Raman spectrum exhibits only one strong band at 700 cm–1, which shifts to higher frequencies with increasing Al content. Gorerite crystallises in the P63/mmc space group, with lattice parameters a = 5.8532(4) Å, c = 22.7730(2) Å and V = 675.67(7) Å3 with Z = 2. It exhibits a structure characterised by an intercalation of triple spinel-like S blocks and rock-salt type R blocks along the hexagonal c-axis.