Ksar Ghilane 023 Ungrouped Achondrite

Petrography: This meteorite is a highly reduced coarse grained Mg-rich clinopyroxenite composed predominantly of endmember augite (perhaps better described as subcalcic diopside) ~92.5 vol.% with minor enstatite ~7.5% vol.% and accessory aubrite-like sulfides. Enstatite occurs as small anhedral and subhedral grains poikilitically enclosed within clinopyroxene. Enstatite is also found as fine exsolution lamellae within clinopyroxene grains. Sulfides are troilite, alabandite, daubréelite, caswellsilverite, and oldhamite occurring as monophase and polyphase immiscible spheroids ranging from approximately 5 to 50 µm within clinopyroxene grains. A single small grain of low-Ni kamacite was found and confirmed with EDS. No olivine or plagioclase were detected.

Geochemistry: Augite Fs_0.0-0.1Wo_37.4-40.9 (N=39), enstatite Fs_0.0-0.1Wo_0.9-3.6 (N=20). Alabandite Mn=45.9±1.8 wt%, S=36.3±0.4 wt%, Fe=15.8±1.8 wt% (N=19). Daubréelite S=43.2±0.5 wt%, Cr=34.2±0.6 wt%, Fe=18.2±0.9 wt% (N=39). Caswellsilverite S=43.9±0.2 wt%, Cr=35.5±0.1 wt%, Na=14.8±0.01 wt% (N=2). Oldhamite Ca=54.3 wt%, S=41.5 wt% (N=1). Oxygen isotopes (R. Greenwood, OU): analyses of acid-washed subsamples by laser fluorination gave, respectively, δ¹⁷O 2.906, 2.931; δ¹⁸O 5.521, 5.547; Δ¹⁷O 0.009, 0.020 per mil (all data linearized, TFL slope = 0.5247).