Merweville:A new South African chondritic meteorite

Abstract

We report petrologic, petrographic and chemical data for a newly discovered meteorite specimen from South Africa. The 7.04 kg specimen was found in ca. 1977 on the farm Waterval 64, about 30 km from the town of Merweville (−375 km northeast of Cape Town). Our research group confirmed the identity of the stone as a meteorite in 1997, and obtained a ~1.5 kg portion for study and classification. Externally, the specimen shows a few regmaglypts and a reddish-brown, weathered fusion crust. The sawn internal surfaces show that terrestrial weathering effects, which render a dark brownish colour to the specimen, have penetrated up to 4 to 5 cm into the meteorite. The relatively unweathered interior is light orange-brown in colour. Petrographically, the specimen shows a dominantly recrystallised texture, with a few recognisable chondrules or chondrule fragments. Shock stage is estimated at S2, and weathering grade is W2. Microprobe analyses yield: olivine (Fa23.32 ±0.612, PMD = 0.52, n = 13), orthopyroxene (Fs20.59 ±0.54, n 15), kamacite (Ni = 6.48 ± 0.24 wt.%, Co = 0.94 ± 0.14 wt.%, n = 15), taenite (Ni = 28.9 ± 2.3 wt.%, Co = 0.29 ± 0.08 wt.%, n = 3), troilite (Ni = 0.10 ±0.11 wt.%, n = 17) and chromite (Cr/(Cr+Al) = 0.860 ± 0.003, n = 4). No recognisable feldspar or glass is present in our thin sections of Merweville The dominantly recrystallised but partial preservation of chondrules, apparent absence of glass, and the relative uniformity of olivine and pyroxene compositions are all consistent with classification of Merweville as petrologic type 5. Chemical and mineralogical data for the “unweathered” portion of the meteorite fall best within the L group. We conclude that Merweville is an L5 chondrite. This new specimen increases the inventory of known South African meteorites to a total of 48.