Experimentelle und Analytische Planetologie
TEM investigations of Mysterite
The microstructure and composition of the matrix of one carbonaceous inclusion (K1) in the Krymka LL3.1
chondrite have been studied by using transmission electron microscopy (TEM). K1 has previously shown an
enigmatic nature and similarities with volatile-rich, fine-grained, dark inclusions of Krymka called
mysterite. In the present
study, four minerals were identified with TEM. Olivine, pyroxene, and pyrrhotite have grain sizes of typically
one micrometer, graphite occurs as flakes with similar size. Olivine shows a moderately high dislocation density
most probably caused by shock. Pyroxene shows coexisting ortho- and clinoenstatite lamellae that probably
originated from shear stress after a shock event or from rapid cooling from the protoenstatite stability field.
However, we demonstrate that in this case a shock trigger is more likely. Pyrrhotite in the studied sample occurs
as a 4C monoclinic superstructure. The graphite flakes in the fragment are well crystallized, as can be seen by
discrete spots in the diffraction pattern. In graphite the degree of crystallization increases with the metamorphic
grade. Based on the microstructure of this mineral we conclude that after a first moderate shock event the
residual temperature between 300°C and 500°C led to thermal metamorphism. A second shock event,
possibly at excavation from the parent body, is responsible for the observed shock features in olivine,
pyroxene, and graphite.
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