New minerals tsangpoite, matyhite and kuratite from angrite D’Orbigny

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Marco E. Ciriotti
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New minerals tsangpoite, matyhite and kuratite from angrite D’Orbigny

Messaggio da Marco E. Ciriotti » mar 14 ago, 2018 11:58

▪ Hwang, S.-L., Shen, P., Chu, H.-T., Yui, T.-Fu,, Iizuka, Y., Varela, M.-E. (2018): New minerals tsangpoite, matyhite and kuratite from angrite D’Orbigny. IMA2018 Abstract book. Poster presentations. Meteorites and the Early Solar System, 433.

Tsangpoite, ideally Ca5(PO4)2(SiO4), the hexagonal polymorph of silicocarnotite, matyhite, ideally Ca9(Ca0.5□0.5)Fe(PO4)7, the Fe-analogue of Ca-merrillite, and kuratite, ideally Ca4(Fe2+10Ti2)O4[Si8Al4O36], the Fe2+-analogue of rhönite, were identified from the D'Orbigny angrite meteorite by electron probe microanalysis, electron microscopy and micro-Raman spectroscopy. Based on electron diffraction, the symmetry of tsangpoite was shown to be hexagonal, P63/m or P63, with a = 9.489 ± 0.004 Å, c = 6.991 ± 0.006 Å, V = 545.1 ± 0.6 Å3 and Z = 2 for 12 oxygen formula, that of matyhite was shown to be trigonal, R3c, with a = 10.456 ± 0.007 Å, c = 37.408 ± 0.034Å, V = 3541.6 ± 4.8 Å3 and Z = 6 for 28 oxygen formula, and that of kuratite was shown to be triclinic (space group P by analogy to rhönite) with a = 10.513(7), b = 10.887(7), c = 9.004(18)Å, α = 105.97(13), β = 96.00(12), γ = 124.82(04)o, V = 767 ± 2 Å3 and Z = 1 for the 40 oxygen formula. Based on their constant association with grain boundary assemblage: Fe-sulfide + ulvöspinel +Al-Ti-bearing hedenbergite + fayalite-kirschsteinite intergrowth, the formation of these new minerals can be readily rationalized by crystallization from residue magmas at the final stage of D’Orbigny formation. Alternatively, the close petrographic relations between tsangpoite/matyhite and the resorbed Fe-sulfide rimed by Fa+Kir 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 + 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 angrite D’Orbigny.
Marco E. Ciriotti

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