[meteorite-list] Benenitra meteorite fall is now official

From: Galactic Stone & Ironworks <meteoritemike_at_meteoritecentral.com>
Date: Fri, 12 Apr 2019 15:49:50 -0400
Message-ID: <CAKBPJW_bBmh8RGVaubkT=fP=q2bomPmQBrg1+AS-0uGLfPd7uw_at_mail.gmail.com>

The Benenitra meteorite fall is now official.


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 ?m 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
?m 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 ?m thick.

Geochemistry: Mineral compositions: (L.D. Ashwal and A. Ziegler)
Olivine (Fa24.0?0.8), low-Ca pyroxene (Fs20.4?0.9Wo1.4?0.4), high-Ca
pyroxene (Fs8.0? 0.8Wo42.4?1.0), feldspar
(Ab79.1?3.1An13.3?1.9Or7.6?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.

Link - https://www.lpi.usra.edu/meteor/metbull.php?code=69345

All 21st Century Witnessed Falls - http://galactic-stone.com/pages/falls

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Received on Fri 12 Apr 2019 03:49:50 PM PDT