Northwest Africa 12971 (NWA 12971)

(Northwest Africa)

Purchased: 2019 Apr

Classification: Lunar (troctolitic melt rock)

History: Purchased jointly by Craig Zlimen, Mark Lyon and Matthew Stream in April 2019 from a Moroccan dealer.

Physical characteristics: A single light gray stone (280 g) with visible vesicles and light brown weathering products on one side. The fresh interior is composed predominantly of vesicular melt rock which contains some clast-like regions of coarser grained melt rock.

Petrography: (A. Irving, UWS and P. Carpenter, WUSL) Very fine-grained (grainsize up to 5 µm), microvesicular melt-textured specimen composed predominantly of anorthite plus subordinate olivine and accessory pigeonite, augite, chromite (exhibiting zoning from Ti-bearing cores to Ti-free rims), troilite and pyrrhotite. No intact clasts were observed anywhere in the entire 5 cm diameter slice examined by microprobe imaging, but there are sporadic coarser-grained (up to 40 µm) melt-textured regions.

Geochemistry: Anorthite (An_97.2-97.7Or_0.0, N = 2), olivine (Fa_24.9-35.5, FeO/MnO = 77-99, N = 6), magnesian olivine core (Fa_19.0, FeO/MnO = 98), ferroan olivine rim (Fa_38.3, FeO/MnO = 80), pigeonite (Fs_26.2Wo_19.4, FeO/MnO = 44), augite (Fs_19.8-35.1Wo_35.5±0.0, FeO/MnO = 43-55, N =2).

Classification: Lunar (troctolitic melt rock). The predominance of anorthite and olivine indicates a troctolitic bulk composition. The texture and apparent absence of clasts are consistent with crystallization from a totally molten state.

Specimens: 22.3 g in the form of a large polished slice at UWB; remainder with Mr. C. Zlimen, Mr. M. Lyon and Mr. M. Stream.