Northwest Africa 8383 (NWA 8383)

(Northwest Africa)

Purchased: 2013

Classification: HED achondrite (Eucrite, cumulate)

History: Single stone acquired by Ruben Garcia at the 2013 Denver mineral show and donated to CMS.

Physical characteristics: Single, 24.9 g, glossy fusion-crusted stone. Minor weathering. Sawn surface shows coarsely crystalline interior dominated by mm-sized light greenish-gray pyroxene crystals (roughly 85%), interstitial glassy to white plagioclase (roughly 15%), with a smattering of fine opaques.

Petrography: Thin section and microprobe examination shows coarse-grained cumulate basalt composed of intercumulus irregularly-shaped plagioclase (to 5 mm in the long dimension), with cumulate pyroxene (<3 mm). Most pyroxenes show fine (<1 μm) exsolution lamellae. Silicates highly fractured and show undulatory extinction and mosaicism. Chromite with two size ranges: scattered and sparse 100 to 500 μm, and ubiquitous fine grained, typically 10 μm. Rare troilite and Fe-metal to 20 μm. Some melt veins and fractures with small-scale brecciation are present, and range in width from a few tens of microns to ~100 microns across.

Geochemistry: (K. Tucker, J. Lagerman, A. Pena and L. Garvie, ASU) Low Ca-pyroxene Fs_35.3±0.5Wo_3.1±1.0, Fe/Mn=32.4, n=8; augite-diopside Fs_14.0±0.7Wo_45.0±0.4, Fe/Mn=26.6±2.0, n=5; and plagioclase An_89.6±1.6Or_0.4±0.1, n=5.

Classification: Achondrite (cumulate eucrite).

Specimens: 20.28 g and one polished thin section at ASU.