Petrography and classification of NWA 7402: A new sulfide-rich unequilibrated ordinary chondriteOPEN ACCESS
Christine E. Jilly-Rehak, Gary R. Huss, Lydie Bonal, Eric Twelker
Chemie der Erde – Geochemistry
doi:10.1016/j.chemer.2016.01.001
Received 26 January 2015, Revised 1 September 2015, Accepted 4 January 2016, Available online 23 January 2016
“We classify a new chondritic find Northwest Africa (NWA) 7402. This meteorite is highly unequilibrated, and is therefore potentially significant for the study of primitive Solar System materials. Mineralogy, mineral chemistry, and modal abundances of minerals indicate that NWA 7402 is most likely an L chondrite. However, the specimen contains a higher abundance of sulfide than commonly seen in ordinary chondrites. The structural order of organic matter in the matrix and the chromium content of Fe-rich olivine grains indicate a petrologic type of 3.1. NWA 7402 largely escaped thermal metamorphism, and secondary phases formed by aqueous alteration are rare to absent. Minor planar fractures and undulatory extinction of olivine grains suggest that NWA 7402 experienced shock up to stage 2 or 3. Terrestrial weathering is heterogeneous in the specimen; much of the stone’s exterior shows substantial Fe oxidation (weathering grade 2), while some parts of the interior remain relatively fresh (weathering grade 1). NWA 7402 has some unusual features that should be investigated further. The sulfide abundance is higher than reported sulfide contents for other L chondrites, and the chromium content of the olivines does not fall on the trend established for unequilibrated ordinary chondrites by Grossman and Brearley (2005).”
