NORTHWEST AFRICA 8777


Achondrite, ungrouped
Olivine-orthopyroxenite
standby for nwa 8777 photostandby for nwa 8777 photo
Purchased Oct 2013
no coordinates recorded

A single relatively unweathered meteorite weighing 49.1 g was found in Northwest Africa and subsequently purchased by S. Ralew from a Moroccan dealer. A sample was sent for analysis and classification to the University of Washington in Seattle (A. Irving and S. Kuehner), including an oxygen isotope analysis at the University of New Mexico (K. Ziegler; MetBull plot), and NWA 8777 was classified as an ungrouped achondrite.

Northwest Africa 8777 is an olivine-orthopyroxenite composed of orthopyroxene (88.6 vol%) and olivine (9.0 vol%) along with minor calcic plagioclase (bytownite; An77.378.8) and accessory Al-bearing chromite, Ni-poor kamacite, and troilite (Irving et al., 2015 #5254). The meteorite shows some similarities to the brachinites, including a recrystallized metamorphic texture with 180° triple grain junctions and an oxygen isotope composition plotting close to the brachinite field (see diagram below). However, its low abundance of olivine and calcic plagioclase exclude it from this group, and NWA 8777 is considered to be a unique ungrouped achondrite.

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click on image for a magnified view

Diagram credit: Greenwood et al., Chemie der Erde—Geochemistry, vol. 77, p. 23 (2017, open access link)
'Melting and differentiation of early-formed asteroids: The perspective from high precision oxygen isotope studies'
(http://dx.doi.org/10.1016/j.chemer.2016.09.005)

Further study is needed to better assess the petrogenetic history of this achondrite. The specimen of NWA 8777 shown above is a 0.463 g partial slice acquired from Mendy Ouzillou of SkyFall Meteorites, previously obtained from Stefan Ralew of SR–Meteorites. The photo below better exhibits the full-scale details of this unique achondrite in a 1.309 g specimen, shown courtesy of Stefan Ralew.

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Photo courtesy of Stefan Ralew—SR–Meteorites