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

Abstract

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.

Neutron and XRD Single-Crystal Diffraction Study and Vibrational Properties of Whitlockite, the Natural Counterpart of Synthetic Tricalcium Phosphate

“…The unit cell parameters from neutron and X-ray diffraction measured for the present sample are in the range of those observed in other natural samples from whitlockite and merrillite subgroups from the literature (Table 4). [34]; n ideal chemical formula [35]; o [7].…”

“…Besides the Fe 2+ presence at the M site, the samples were described as heavily deformed for the shock events during the entry in the atmosphere [34]. Minor details are available for mathyite, ideally Ca 9 (Ca 0.5 0.5 )Fe 2+ (PO 4 ) 7 , characterized by the absence of Na at the A(1,2,3) sites, and reported as the product of metasomatic process in the D'Orbigny angrite meteorite [35].…”

The impact history and prolonged magmatism of the angrite parent body

“…The high‐angle grain boundaries present in phosphates within NWA 7203 are indicative of recrystallization, implying that phosphates have undergone Pb loss and diffusion, resulting in the phosphate 207 Pb‐ 206 Pb date recording the timing of impact, rather than the original crystallization. It is noted, however, that these phosphates may not experience Pb diffusion identical to apatite and merrillite due to their chemical and structural differences (Hwang et al., 2019). The ancient date of 4562 ± 9.3 Ma obtained on NWA 7203 phosphates is very similar to the crystallization ages of other quenched angrites, suggesting that these phosphates have retained radiogenic Pb, or that the phosphates record an ancient impact event, within uncertainties of the crystallization of the quenched angrites.…”

“…Angrites are medium‐ to coarse‐grained basaltic igneous rocks consisting of variable proportions of calcic olivine, Al‐Ti‐bearing diopside–hedenbergite, and anorthite (Keil, 2012). Minor and accessory phases within angrites are kirschsteinite, spinel, ulvöspinel, metallic FeNi, troilite, titanomagnetite, whitlockite, ilmenite, celsian, rhönite, kuratite (the Fe 2+ analog of rhönite—Ca 4 [FTi 2 ][O 4 Si 8 Al 4 O 36 ]) and silico‐phosphates (Hwang et al., 2016, 2019; Keil, 2012). Most noticeably, angrites contain phosphates (silico‐phosphate), which can host uranium and are thus key phases for in situ dating using the U to Pb radioactive decay system.…”

“…Most noticeably, angrites contain phosphates (silico‐phosphate), which can host uranium and are thus key phases for in situ dating using the U to Pb radioactive decay system. The phosphates present in angrites are tsangpoite Ca 5 (PO 4 ) 2 (SiO 4 ) (the hexagonal polymorph of silicocarnotite) and matyhite Ca 9 (Ca 0.5 □ 0.5 )Fe(PO 4 ) 7 (the Fe‐bearing analog of Ca‐merrillite) (Hwang et al., 2019), which are very similar in terms of chemistry and structure to apatite Ca 5 (PO 4 ) 3 (F, Cl, OH) and merrillite Ca 9 Na(Fe,Mg)(PO 4 ) 7 (Hughes & Rakovan, 2002; Hughes et al., 2006; Hughes, 2015; Xie et al., 2015). Apatite and merrillite exhibit microstructures that progressively become more complex and deformed with increasing levels of shock‐loading in terrestrial settings, lunar, Martian, and eucrite meteorites (e.g., Černok et al., 2019; Cox et al., 2020; Darling et al., 2016, 2021; McGregor et al., 2021; White et al., 2021).…”