Achondrite ung - NWA 13272

NWA 13272 pairing

Northwest Africa 13272 (NWA 13272)

Place of discovery: Northwest Africa

Purchased: 2019 Dec

Classification: Ungrouped achondrite

History: Found in Mauritania and purchased by Rachid and Jaouad Chaoui in December 2019 from a dealer in Zouerat, Mauritania.

Physical characteristics: The specimen lacks fusion crust and is coated by a shiny brown desert patina. Polished interior surfaces reveal the presence of rare tiny specks of partially altered metal.

Petrography: (A. Irving, UWS and P. Carpenter, WUSL) The specimen has a fine grained, poikilitic igneous texture. Composed predominantly of polysynthetically-twinned, compositionally-zoned pyroxene oikocrysts (with domains of orthopyroxene, pigeonite and subcalcic augite) enclosing chadacrysts of olivine, together with interstitial devitrified silicic glass (pale pink in thin section) plus accessory troilite (some Cr-bearing), Ti-poor chromite and very rare kamacite (some altered to Fe hydroxides). Olivine is preferentially stained pale orange in thin section, and there are some cross-cutting dilation veins filled with comminuted olivine and orthopyroxene. Minor secondary calcite and anhydrite are present.

Geochemistry: Olivine (Fa24.0-29.5, N = 8), orthopyroxene (Fs17.9-19.0Wo2.0-3.8, N = 5), pigeonite (Fs18.9-19.0Wo7.2-9.0, N = 2), subcalcic augite (Fs12.2-12.6Wo33.7-37.1, N = 4). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed bulk subsamples by laser fluorination gave, respectively, δ17O 4.120, 4.159, 4.045; δ18O 5.908, 6.096, 5.717; Δ17O 1.001, 0.940, 1.026 per mil.

Classification: Achondrite (ungrouped, igneous, with oxygen isotopic affinity to L chondrites).

Mass (g): 1603

Pieces: many

Class: Achondrite-ung

Shock stage: low

Weathering grade: low to medium

Magnetic suscept.: 3.49

Classifier: A. Irving, UWS, and P. Carpenter, WUSTL

Main mass: R. Chaoui/J. Chaoui


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