Northwest Africa 12562 (NWA 12562)

Algeria

Find: 2017

Classification: Ungrouped achondrite

History: A single stone (3930 g), reportedly found in Algeria in 2017, was purchased in Chenzhou, China, by Zuokai Ke in May 2018.

Physical characteristics: Single stone, with a small patch of fusion crust. The surface reveals a fragmental breccia with coarse cream-colored to pale-green grains up to 1 cm in size, crosscut by fine dark veinlets and surrounded by finer-grained light to dark-gray material. Some small clasts are stained by oxidation.

Petrography: (X. Gu, CSUC) The meteorite is composed of brecciated fragments of olivine (85%), pyroxene (8%), and plagioclase (5%), with accessory phases troilite (1%), tridymite (0.4%), chromite(0.3%), and kamacite and taenite (0.2%). The rock-forming minerals are euhedral with grain size generally between 100-800 μm, with some up to several mm. Grains are unzoned. Some material is brecciated to fragments of 10-50 μm. Vermicular chromite-pyroxene symplectites and exsolution lamellae of orthopyroxene-augite are common. Trace alkali feldspar, schreibersite, pentlandite, merrillite, fluorapatite, and ilmenite are observed.

Geochemistry: (X. Gu, CSUC) Plagioclase An_2.6-84.6Or_0.2-4.7Ab_14.8-92.8 (average: An_60.6±24.8Or_1.6±1.8Ab_37.8±23.7, n=85); olivine Fa_7.3-94.1 (average Fa_17.8±24.0, n=137), Fe/Mn=33.9-64.2 (average=42.9±6.9); low-Ca pyroxene Fs_8.0-68.0Wo_1.3-8.5 (average Fs_29.5±16.4Wo_3.5±1.6, n=78), Fe/Mn=21.5-35.6 (average=30.5±2.8); high-Ca pyroxene Fs_3.1-65.9Wo_9.0-47.2 (average Fs_28.4±17.4Wo_36.5±10.0, n=42). (Z. Vaci, UNM) Olivine Fa_17.0±11.6, Fe/Mn=40±3, n=63; low-Ca pyroxene Fs_27.3±10.4Wo_4.1±2.4, Fe/Mn=28±1, n=17; high-Ca pyroxene Fs_37.9±9.6Wo_8.3±6.1, Fe/Mn=27±2, n=7, chromite Al₂O₃=7.2±4.8, Cr₂O₃=58.4±6.0, MgO=5.0±1.1, MnO=0.7±0.1, FeO=25.7±2.1 TiO₂=0.7±0.4 (wt%), n=6. Oxygen isotopes (K. Ziegler, UNM): 3 acid-washed fragments analyzed by laser fluorination gave δ¹⁸O= 3.477, 3.492, 3.795; δ¹⁷O= 1.609, 1.619, 1.788; Δ¹⁷O= -0.227, -0.225, -0.216 (linearized, all per mil, TFL slope=0.528).

Classification: Ungrouped achondrite, dunite breccia. This meteorite is possibly a polymict breccia in that the dominant mineral fragments are mostly unzoned, but when individually sampled by microprobe analysis display a wide compositional range. The oxygen isotope values of this meteorite plot slightly higher than the eucrite fractionation line (EFL) and are also in the vicinity of the brachinites. The Fe/Mn of this meteorite is somewhat lower than found in HEDs and much lower than in angrites. Unlike most HEDs, it contains alkali feldspar and a wide range of plagioclase compositions. The range in olivine composition in this meteorite is much larger than found in the brachinites and it has much lower Fe/Mn than brachinites. Its mineralogy, oxygen isotopic composition, and secondary features such as Cr-symplectites are similar to the ungrouped dunitic achondrite NWA 12217, but its minerals show a much greater range in major element composition. It is also more extensively brecciated, with heavy fracturing and clast size ranging from μm to cm scale.

Specimens: 21 g including a probe mount on deposit at UNM, Zuokai Ke holds the main mass.