无球粒陨石端切面（未分组，富含镁的单斜辉石岩） 吉兰堡 022 - 1.21 g - (1)

Ksar Ghilane 022 (KG 022) 32.559°N, 9.508°E

Tatawin, Tunisia

Purchased: 2023

Classification: Ungrouped achondrite

Physical characteristics: A single large stone (25 kg) and many smaller pieces found with it. Most of the stones lack fusion crust and have mottled, dark and light gray granular exteriors. However, several pieces are partly coated by black fusion crust. The interiors of the stones have the appearance of equigranular aggregates of light gray and whitish grains.

Petrography: (A. Irving, UWS, and P. Carpenter, WUSL) The specimen is composed predominantly (>90 vol.%) of almost end-member augite (mostly as equant grains, mean grainsize ~1.5 mm) accompanied by minor enstatite and accessory Cr-troilite, daubreelite, alabandite and an Mn-Fe oxide phase. Enstatite occurs as small irregular inclusions or sparse fine lamellae within augite grains, and different macroscopic colors of the augite grains apparently reflect differing concentrations of sulfide inclusions. Some secondary calcite veins are present throughout.

Geochemistry: Augite (Fs0.0-0.1Wo39.4-42.3, N = 3), enstatite (Fs0.1±0.0Wo0.9-3.6, N = 3). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed subsamples by laser fluorination gave, respectively, δ17O 3.018, 2.926; δ18O 5.781, 5.559; Δ17O -0.034, -0.009 per mil (all data linearized, TFL slope = 0.528).

Classification: Achondrite (ungrouped, Mg-rich clinopyroxenite). This meteorite is texturally and mineralogically very similar to ungrouped augite-rich achondrite NWA 15915. but does not exhibit the same degree of irrational exsolution of enstatite from the dominant constituent augite. Terrestrial pairing is further excluded by the different physical appearance of these two meteorites, different degree of weathering, and the fact that their purported find sites are hundreds of kilometers apart. Both of these meteorites may have some affinities to aubrites, but differ in being composed predominantly of almost Fe-free augite rather than enstatite.