Northwest Africa 8404 (NWA 8404)

(Northwest Africa)

Purchased: 2014

Classification: HED achondrite (Diogenite, olivine)

History: Purchased by J. Wooddell from a Moroccan dealer, 2014 Feb 7, at the Tucson Gem and Mineral Show.

Physical characteristics: Single stone fragment with dull moderately weathered black fusion crust covering 35% of the stone. Broken surface and saw cut reveal numerous mm-sized green crystals set in light yellow groundmass.

Petrography: Microprobe examination of a polished mount shows a brecciated texture with large pyroxene grains 300-2000 μm and smaller olivine grains 100-500 μm, many grains are fragmental to cataclastic. Accessory plagioclase, iron metal, and troilite. Minor amounts of iron oxidation.

Geochemistry: (C. Agee and N. Muttik, UNM) EMPA. Low Ca-pyroxene Fs_25.0±0.3Wo_3.3±0.3, Fe/Mn=30±1, n=13; olivine Fa_26.8±0.3, Fe/Mn=49±3, n=9; plagioclase An_88.2±3.0Ab_11.4±2.9Or_0.4±0.2, n=4. (Karen Ziegler, UNM) Oxygen isotope values of 3 acid-washed aliquots of bulk sample, 1.0, 1.7, 1.8 mg, gave δ¹⁷O = 1.510, 1.328, 1.452, δ¹⁸O = 3.477, 3.103, 3.233, Δ¹⁷O = -0.326, -0.310, -0.255 (linearized, all permil).

Classification: Achondrite (Diogenite-olivine) based on the presence of approximately 25% olivine. Typical δ¹⁸O values for diogenites, however two analyses gave anomalously low values for Δ¹⁷O.

Specimens: 16.1 g plus a thin section on deposit at UNM, J. Wooddell holds the remainder and a mount.