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- Title
Chenmingite, FeCr<sub>2</sub>O<sub>4</sub> in the CaFe<sub>2</sub>O<sub>4</sub>-type structure, a shock-induced, high-pressure mineral in the Tissint martian meteorite.
- Authors
Ma, Chi; Tschauner, Oliver; Beckett, John R.; Liu, Yang; Greenberg, Eran; Prakapenka, Vitali B.
- Abstract
Chenmingite (FeCr2O4; IMA 2017-036) is a high-pressure mineral, occurring as micrometer- to submicrometer-sized lamellae within precursor chromite grains along with xieite and Fe,Cr-rich ulvöspinel next to shock-induced melt pockets, from the Tissint martian meteorite. The composition of type chenmingite by electron probe analysis shows an empirical formula of ( Fe 0.75 2 + Mg 0.23 Mn 0.02 ) $\left(\text{Fe}_{0.75}^{2+}\text{M}{{\text{g}}_{0.23}}\text{M}{{\text{n}}_{0.02}} \right)$ ( Cr 1.60 Al 0.29 Fe 0.06 3 + Fe 0.04 2 + Ti 0.02 ) Σ 2.01 O 4. ${{\left(\text{C}{{\text{r}}_{1.60}}\text{A}{{\text{l}}_{0.29}}\text{Fe}_{0.06}^{3+}\text{Fe}_{0.04}^{2+}\text{T}{{\text{i}}_{0.02}} \right)}_{\Sigma 2.01}}{{\text{O}}_{4}}.$ The general and end-member formulas are (Fe,Mg)(Cr,Al)2O4 and FeCr2O4. Synchrotron X‑ray diffraction reveals that chenmingite has an orthorhombic Pnma CaFe2O4-type (CF) structure with unit-cell dimensions: a = 9.715(6) Å, b = 2.87(1) Å, c = 9.49(7) Å, V = 264.6(4) Å3, and Z = 4. Both chenmingite and xieite formed by solid-state transformation of precursor chromite under high pressure and high temperature during the Tissint impact event on Mars. The xieite regions are always in contact with melt pockets, whereas chenmingite lamellae only occur within chromite, a few micrometers away from the melt pockets. This arrangement suggests that chenmingite formed under similar pressures as xieite but at lower temperatures, in agreement with experimental studies.
- Subjects
ELECTRON probe microanalysis; MARTIAN meteorites; METEORITES; MINERALS; CHROMITE; HIGH temperatures; LOW temperatures; SIDEROPHILE elements
- Publication
American Mineralogist, 2019, Vol 104, Issue 10, p1521
- ISSN
0003-004X
- Publication type
Article
- DOI
10.2138/am-2019-6999