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A new classification of Nyirábrany, an ordinary chondrite from Hungary

Mészáros M., Kereszturi A., Ditrói-Puskás Z.

Meteorites

2014

Vol. 3, No. 1-2

19--32

The Nyirábrany meteorite is an ordinary chondrite from Hungary that fell in 1914 and, to date, has been studied very little. The aim of this work was to carry out a more detailed examination of this meteorite (using optical polarization microscope, energy dispersive X-ray spectroscopy and Raman micro spectroscopy) and re-investigate its previous classification as an LL5 type ordinary chondrite, moreover to complete its classification with a shock stage and a weathering grade. Our new results indicate that Nyirábrany could be a transition type between the L and LL chondrites. The main mineral phases of Nyirábrany are olivine, pyroxene and opaque minerals (e.g. Fe-Ni metal, troilite, chromite), minor constituents are plagioclase, Cl-apatite, cristobalite and glass. The Fe-Ni metal content (1.32 vol%) of Nyirábrany is typical of the LL group, the Fa content of olivines (26.71 mol%) is between the range of the L and LL types, while the Fs-content of the low-Ca pyroxenes (20.51 mol%) is typical of the L-chondrites. Chondrules appear in different sizes, mineral compositions and textures. The textural and mineralogical features (e.g. mostly homogeneous silicate minerals, dominance of clinopyroxenes, recrystallized matrix, well-defined chondrules) indicate petrological type 4-5 for Nyírábrány. The shock stage and the weathering grade of this meteorite were examined for the first time. On the basis of the observed optical and textural features of the olivine grains (e. g. sharp optical extinction, irregular and planar fractures) Nyirábrany has an S2 shock stage. About 30–40% of the opaque phases are affected by oxidation, which shows a W2 weathering grade.