Northwest Africa 16720 (NWA 16720)

(Northwest Africa)

Purchased: 2024

Classification: Lunar (feldsp. melt rock)

History: The specimen was found probably in Algeria by an anonymous hunter. Portions of the mass totaling 34.4 g were acquired in December 2023 by Ziyao Wang and Aziz Zad and provided as type material for classification at UWS. Subsequently the main mass was purchased by Abdelhadi Aithiba and an additional 24.7 g type sample provided for classification.

Physical characteristics: A single large stone (9390 g) coated by a greenish-tan patina and exhibiting degraded regmaglypts on some exterior surfaces. The fresh interior is extremely fine-grained and overall light gray in color.

Petrography: (A. Irving, UWS, and P. Carpenter, WUSL) Ultra fine-grained, micropoikilitic specimen (mean grainsize ~50 µm) composed of tiny grains of anorthite (all converted to maskelynite), pigeonite oikocrysts, olivine and subcalcic augite, together with accessory ilmenite, Ti-chromite, troilite, taenite, fluorapatite and baddeleyite. Rare angular mineral fragments (up to 1 mm in size) are present.

Geochemistry: Olivine (Fa_39.1-41.4, FeO/MnO = 86-113, N = 11), pigeonite (Fs_28.1-31.2Wo_14.2-10.6, FeO/MnO = 49-59, N = 7), subcalcic augite (Fs_25.0-25.7Wo_24.5-20.1, FeO/MnO = 52-58, N = 2), anorthite (An_94.1-97.1Or_0.3-0.1, N = 10).

Classification: Lunar (feldspathic melt rock, ultra fine-grained). The extremely fine grain size of this specimen and presence of accessory taenite suggest that it is a product of impact melting followed by very rapid crystallization.

Specimens: 69.1 g including one polished thin section and one polished mount at UWB; main mass with Mr. A. Aithiba.