Benenitra        23°26.786’S, 45°4.692’E

Toliara, Madagascar

Confirmed fall: 27 July 2018

Classification: Ordinary chondrite (L6)

History: Reports of a meteor that detonated in a loud explosion, and stones falling from the sky into the town of Benenitra (pop. ~30,000) on the evening of July 27, 2018, were received by a visiting geologist, Timothy Marais, on July 30, 2018. He was shown photographs and several small fragments, two of which he purchased, weighing 99 and 14 g. Roger Gibson and Lewis Ashwal in the School of Geosciences at the University of the Witwatersrand confirmed a meteorite origin for these specimens using petrographic analysis and EMPA. Confirmation of the date and time of the fall was obtained independently when an upper atmosphere infrasound event was identified on a bearing south-southwest of the CTBTO station IS33 near Antananarivo, Madagascar, at 17h16 GMT on July 27 by Dr. Andry Ramanantsoa (Laboratory of Seismology and Infrasound, University of Antananrivo). A weak ground tremor at approximately 17h17 GMT was identified in the data from the seismograph at the Sakaraha (SKRH) station approximately 80 km northwest of Benenitra by Dr Ranto Raveloson (Wits), and was interpreted to be related to the airburst. Magnetic susceptibility measurements were performed by Prof. Susan Webb (Wits).

Physical characteristics: Two broken fragments containing small remnants of bluish-black to brown-black fusion crust and weighing 14 g and 82 g (after thin sectioning) consist of a light-gray matrix with disseminated metal (<1 mm) and some visible chondrules (<5 mm). The edge of the larger fragment, which contains a thin (<0.5 mm), dark-gray melt vein, was sectioned. Photographs taken by local residents show more than a dozen other fragments ranging in mass from ~100-1000 g; these show mostly intact fusion crusts with only limited chipping of edges. Samples range from subangular to subrounded to disc-shaped, with both sharp and rounded edges. Fusion crusts on these samples are generally smooth, with a few shallow regmaglypts.

Petrography: (L.D. Ashwal and R.L. Gibson, Wits) Modal abundances: 50% olivine, 25% low-Ca pyroxene, 5% high-Ca pyroxene, 10% feldspar, 7% troilite, 2% kamacite, 1% taenite, and trace amounts of chromite and a silica-rich phase. Recognizable chondrules range in size between 1 and 4.5 mm in diameter, and include porphyritic olivine and/or pyroxene, barred olivine, radial pyroxene and cryptocrystalline types, although their original textures have been variably modified by secondary thermal effects. Feldspar is almost entirely crystalline, and occurs as irregular grains up to 100 μm across, many of which display twinning. Pyroxenes are untwinned, and most grains exhibit straight extinction, although minor undulatory extinction is present in some grains. Low-Ca pyroxene shows parallel extinction with respect to cleavage traces. High-Ca pyroxene occurs as irregular grains up to 20 μm across; exsolution lamellae were observed in a few grains. Shock features include planar and irregular fractures in olivine, undulatory extinction in feldspar and pyroxenes, and anastomosing opaque shock veins up to 75 μm thick.

Geochemistry: Mineral compositions: (L.D. Ashwal and A. Ziegler) Olivine (Fa_24.0±0.8), low-Ca pyroxene (Fs_20.4±0.9Wo_1.4±0.4), high-Ca pyroxene (Fs_{8.0± 0.8}Wo_42.4±1.0), feldspar (Ab_79.1±3.1An_13.3±1.9Or_7.6±1.5), troilite (Fe = 63.3±0.2, S = 36.5±0.3), kamacite (Ni = 5.7±0.7; Co = 0.85±0.05), taenite (Ni = 27.8±1.0).

Classification: Ordinary chondrite (L6), Shock level S3, Weathering level W0.

Specimens: 82 g (R.L. Gibson, Wits), 25.8 g at TCU (donated by Rob Wesel), reports of one or more pieces with masses of up to 15 kg are unconfirmed.