Chenmingite, FeCr2O4 in the CaFe2O4-type Structure, a Shock-induced, High-pressure Mineral in the Tissint Martian Meteorite

Document Type

Article

Publication Date

10-25-2019

Publication Title

American Mineralogist

Volume

104

Issue

10

First page number:

1521

Last page number:

1525

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 (Fe0.752+Mg0.23Mn0.02) (Fe0.752+Mg0.23Mn0.02(Cr1.60Al0.29Fe0.063+Fe0.042+Ti0.02)ς2.01O4. (Cr1.60A l0.29Fe0.063+Fe 0.042+Ti0.02)Σ 2.01 O4. 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.

Keywords

Chenmingite; FeCr2O4; High-pressure mineral; Shock-induced phase; Tissint martian meteorite; Shergottite

Disciplines

Astrophysics and Astronomy | Physical Processes | Physical Sciences and Mathematics

Language

English

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