New minerals tsangpoite Ca5(PO4)2(SiO4) and matyhite Ca9(Ca0.5□0.5)Fe(PO4)7 from the D'Orbigny angrite

Tsangpoite, ideally Ca5(PO4)2(SiO4), the hexagonal polymorph of silicocarnotite, and matyhite, ideally Ca9(Ca0.5□0.5)Fe(PO4)7, the Fe-analogue of Ca-merrillite, were identified from the D'Orbigny angrite meteorite by electron probe microanalysis, electron microscopy and micro-Raman spectroscopy. On the basis of electron diffraction, the symmetry of tsangpoite was shown to be hexagonal, P63/m or P63, with a = 9.489(4) Å, c = 6.991(6) Å, V = 545.1(6) Å3 and Z = 2 for 12 oxygen atoms per formula unit, and that of matyhite was shown to be trigonal, R3c, with a = 10.456 (7) Å, c = 37.408(34) Å, V = 3541.6 (4.8) Å3 and Z = 6 for 28 oxygen atoms per formula unit. On the basis of their constant association with the grain-boundary assemblage: Fe sulfide + ulvöspinel + Al-Ti-bearing hedenbergite + fayalite-kirschsteinite intergrowth, the formation of tsangpoite and matyhite, along with kuratite (the Fe-analogue of rhönite), can be readily rationalised as crystallisation from residue magmas at the final stage of the D'Orbigny meteorite formation. Alternatively, the close petrographic relations between tsangpoite/matyhite and the resorbed Fe sulfide rimmed by fayalite + kirschsteinite symplectite, such as the nucleation of tsangpoite in association with magnetite ± other phases within Fe sulfide and the common outward growth of needle-like tsangpoite or plate-like matyhite from the fayalite-kirschsteinite symplectic rim of Fe sulfide into hedenbergite, infer that these new minerals and the grain-boundary assemblage might represent metasomatic products resulting from reactions between an intruding metasomatic agent and the porous olivine-plagioclase plate + fayalite-kirschsteinite overgrowth + augite + Fe sulfide aggregates. Still further thermochemical and kinetics evidence is required to clarify the exact formation mechanisms/conditions of the euhedral tsangpoite, matyhite and kuratite at the grain boundary of the D'Orbigny angrite. Fil: Hwang, Shyh Lung. National Dong Hwa University; República de China Fil: Shen, Pouyan. National Sun Yat-sen Universit; República de China Fil: Chu, Hao-Tsu. Central Geological Survey; República de China Fil: Yui, Tzen-Fu. Institute of Earth Sciences; República de China Fil: Varela, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; Argentina Fil: Iizuka, Yoshiyuki. Institute of Earth Sciences; República de China