Northwest Africa 10658 (NWA 10658)

(Northwest Africa)

Purchased: 2014

Classification: HED achondrite (Eucrite, polymict)

History: A 319 g meteorite was purchased by Michael Farmer from a Moroccan dealer at the 2014 Tucson Gem and Mineral show.

Physical characteristics: Exterior is shiny, pitted and heavily sandblasted. Sawn surface shows a gray matrix hosting abundant rounded to sub-angular clasts up to 1 cm, though most are <2 mm across. Clasts show a range of colors from white to black.

Petrography: (A. Wittmann, L.A.J. Garvie, and C. Fudge ASU) In thin section, the stone exhibits a breccia texture of up to 4 mm angular to sub-rounded clasts. Some areas of the breccia matrix are filled with aphanitic melt containing troilite droplets. Most clasts are pyroxene-rich composed of blocky orthopyroxene crystals with >10 μm-thick lamellae of augite-diopside. The largest clast is a 4 mm plagioclase that poikilitically encloses up to 1 mm orthopyroxene oikocrysts that display 20 μm-thick lamellae of augite-diopside. The largest pyroxene clast is 3 mm long. Another clast component consists of 0.4 mm euhedral pigeonite and augite intergrown with equant, tabular plagioclase crystals riddled with tiny, crystallized melt inclusions. Ilmenite, SiO₂, Cr-Fe-Ti spinel, and troilite are minor mineral components in these clasts. SiO₂ occurs as <0.7 mm clasts and grains that are frequently intergrown with small opaque grains and pyroxene. Raman spectroscopy indicates the presence of coesite coexisting with silica glass in some grains; matrix and/or melt domains surrounding SiO₂ grains show characteristic radial fractures. Accessory components are Cr-Fe-Ti spinel, ilmenite, troilite, and Fe-Ni metal. Most clasts are shocked showing mechanical twinning of pyroxene, plagioclase with planar deformation features, and partial to full transformation to maskelynite.

Geochemistry: (A. Wittmann, ASU) Electron microprobe analysis shows feldspar clasts with An_88-93Or_0.1-0.6, such with abundant crystallized melt inclusions are An_82-87Or_0.7-2.6; typical, blocky orthopyroxene crystals have Mg# 54-55, and are Fs_29-48Wo_2-4, with Fe/Mn 29-35; pigeonite associated with melt-inclusion-rich plagioclase has Mg# 37-38, and are Fs₅₉Wo_5.1-6.3, with Fe/Mn 31-35; augite-diopside has Mg# 69, and are Fs_16-17Wo_44-45, with Fe/Mn 22-24. EDS-analysis suggests Fe-metal contains up to 2 wt% Ni.

Classification: Achondrite (polymict eucrite), components are moderately shocked (S4).

Specimens: 43.2 g and one thin secion at ASU.