Parsa enstatite chondrite: a mineralogical and textural analysis (2014)

Undergraduate: Audrey Horne

Faculty Advisor: Allen Glazner
Department: Geology

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The mineralogy and petrology of Parsa, an EH4 enstatite chondrite, was analyzed with an emphasis on the rare mineral roedderite (K,Na)2(Mg,Fe)5Si12O30) using an SEM, a JEOL Hyperprobe, and a Raman spectrometer. The dominant minerals in Parsa include enstatite (Mg2Si2O6), kamacite (Fe-Ni alloy, >90 wt% Fe), and troilite (FeS), indicating formation under highly reducing conditions. Secondary minerals include taenite (Fe-Ni alloy, >20 wt% Ni) albite (NaAlSi3O8), quartz (SiO2), daubreelite (FeCr2S4), caswellsilverite (NaCrS2), and roedderite. The minerals are fragmented, creating a brecciated texture, with only the primary minerals forming crystals >0.5 mm. All minerals are surrounded by FeO(OH), a weathering product of iron-containing minerals, likely in the goethite phase. Both kamacite and taenite contain up to 15 wt% silicon, with more partitioned into taenite. The kamacite has quartz inclusions; the taenite does not. The strong exsolution of iron and nickel indicates a slow cooling history. Roedderite occurs as elongated euhedral crystals, commonly as inclusions in troilite. All crystals are <15 microns across. K and Na typically occur in a 1:1 atomic ratio with no apparent zoning. Roedderite contained within troilite typically forms euhedral-subhedral, unbrecciated prisms with aspect ratios of ~5; roedderite crystals surrounded by brecciated silicates are typically anhedral. This difference in morphology may reflect differences in the physical properties of the minerals.