1,2Noemi Mészárosová, 1,2Roman Skála, 3Mariana Klementová, 3Lukáš Palatinus, 4Jozef Veselý, 4Petr Harcuba
Meteoritics & Planetary Science, (in Press), 1–14 Link to Article [DOI: 10.1111/maps.70262]
1Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Prague 2, Czech Republic
2Institute of Geology of the Czech Academy of Sciences, Prague 6 – Lysolaje, Czech Republic
3Institute of Physics of the Czech Academy of Sciences, Prague 8, Czech Republic
4Department of Physics of Materials, Faculty of Mathematics and Physics, Charles University, Prague 2, Czech Republic
Published by arrangement with John Wiley & Sons
A transmission electron microscopy (TEM) study of four troilite grains fromenstatite chondrites (Y-691, Y-791790, Y-86004, A-881314) and two grains from aubrites(Y-793592, Mayo Belwa) addressed their crystal structures and nanoscale mineralogicalrelationships. The crystal structure of troilite in enstatite-rich meteorites is predominantlyconsistent with the space group P62c, except for the FeS phase from Mayo Belwa, whichexhibits a complex modulated structure consistent with a trilling of the modulated NCpyrrhotite superstructure. TEM energy-dispersive X-ray spectroscopy (TEM-EDS) analysesconfirmed the incorporation of chromium and titanium into the troilite crystal structure,even in samples containing nanometer-sized daubr´eelite exsolution lamellae (A-881314, Y-793592). Nanometer-sized inclusions of (Mn,Mg,Fe)S monosulfide solid solution occur introilite in Y-791790. Crystallographic orientation relationships between troilite andassociated sulfide phases (daubr´eelite and keilite) indicate semi-coherent intergrowths at thenanoscale. The absence of nanometer-sized daubr´eelite in Y-86004 and Y-791790 suggestsrapid cooling of the Cr-Fe sulfide solution and quenching of the chemical composition ofthe phase stable above 700°C, consistent with the impact melt origin of these meteorites.Additional weak, diffuse diffractions observed in selected area electron diffraction patternsfor troilites from Y-86004, Y-791790, and Y-793592 are attributed to the development ofvacancy ordering with variable periodicity along the c-axis, corresponding to NC-typesuperstructures. The detailed nature of vacancy ordering and the contributions of Cr andTi substitution to the observed superstructure features remain unresolved and requirecomprehensive structure analysis.
