Northwest Africa 8228 (NWA 8228)

(Northwest Africa)

Purchased: 2013 Dec

Classification: Carbonaceous chondrite (CM2)

History: Purchased by Adam Aaronson in Temara, Morocco in February 2014, and subsequently acquired by the Field Museum of Natural History.

Physical characteristics: Exceptionally fresh, very fine-grained black specimen (45 g) found as a group of five fragments.

Petrography: (M. Zolensky, JSC; A. Irving and S. Kuehner, UWS) Abundant matrix-supported chondrules (up to 1 mm across) and sparse angular olivine grains occur in an opaque matrix. The chondrules have thick fine-grained rims, and are very circular in thin section. Most chondrules have been partially to entirely pseudomorphed by serpentine, pyrrhotite, pentlandite, tochilinite, dolomite and Ca carbonate. Discrete olivine grains have thin serpentine rims. The matrix consists of serpentine with accessory pyrrhotite, pentlandite, dolomite and Ca carbonate.

Geochemistry: Olivine in chondrules (Fa_1-2, CaO = 0.1-0.8 wt.%, N = 8), discrete olivine grains (Fa_0.5-0.6, N = 3). Oxygen isotopes (K. Ziegler, UNM): analyses of five acid-washed subsamples by laser fluorination gave, respectively, δ¹⁷O -0.900, -1.715, -1.882, 3.087, 2.853; δ¹⁸O 4.730, 3.136, 4.246, 9.209, 9.117; Δ¹⁷O -3.397, -3.371, -4.124, -1.775, -1.961 per mil.

Classification: Carbonaceous chondrite (CM2)

Specimens: 9.1 g including one polished thin section at UWB; remainder at FMNH.