Raman spectroscopy of various phosphate minerals and occurrence of tuite in the Elga IIE iron meteorite

The Raman spectra of phosphate minerals: apatite, merrillite, panethite, brianite, czochralskiite, maricite, new phosphate with composition of Na2Fe(Mg,Ca)(PO4)(2) and high-pressure phase tuite from the Elga IIE iron meteorite are characterized. Panethite, brianite, czochralskiite and new Na-Fe phosphate were described for the first time. The basic features of all studied phosphates include strong (1) symmetric stretching mode of PO43- ions at 950-990cm(-1), antisymmetric (3) vibrations in the 1000-1175cm(-1) region and weak bands in the 400-500cm(-1) region, which correspond to (2) bending mode and in the 550-640cm(-1) region, related to (4) bending mode. Weak bands at less than 300cm(-1) represent lattice modes. Most of the studied phosphates have three non-equivalent positions of phosphorus atoms in the crystal structures and can be derived from glaserite, K3Na(SO4)(2), arrangement. Two or three of non-equivalent [PO4] tetrahedra typically correspond to two or three strong bands in the region of (1) vibrations. High-pressure mineral tuite has similar composition and was formed after merrillite. P-O vibrations in equivalent [PO4] tetrahedra produce major Raman band of tuite at 972cm(-1). The Elga parent-body experienced a shock pressure of at least 12-15GPa according to minimum pressures of tuite formation in the static high-pressure experiments. This is the first finding of tuite in iron meteorites and the only second finding of high-pressure mineral in them. Copyright (c) 2017 John Wiley & Sons, Ltd.