Northwest Africa 10919 (NWA 10919)

(Northwest Africa)

Purchased: 2016

Classification: HED achondrite (Eucrite, monomict)

History: A 54.5 g stone, half covered in dark fusion crust was acquired by Michael Farmer from a Moroccan meteorite dealer at the 2016 Tucson Gem and Mineral show.

Physical characteristics: Moderately angular, monomict breccia stone with well-developed fusion crust. Sawn surface is light colored with anastomosing pattern of darker shock veins and rounded clasts of unshocked material. Low weathering and sparse iron staining observed.

Petrography: (S. Ray and T. Gabriel, ASU) Typical basaltic texture dominated by roughly equal proportions of pyroxene and plagioclase, with regions showing ophitic texture. Pyroxene commonly with exsolution lamellae (low-Ca lamellae within high-Ca host and vice-versa). In unshocked regions, size of pyroxene grains and plagioclase laths to 800 μm. Plagioclase has abundant 5-10 μm inclusions and many laths feature scalloped margins. Accessories include troilite, ilmenite, chromite, and silica. Sparse Ni-free iron metal grains (about 10 μm) occur with assemblage of accessories. Locally, pyroxene and plagioclase shows undulatory extinction, alteration to glass, and extensive fracturing.

Geochemistry: Low-Ca pyroxene (N=6): Fs _55.8±5.0Wo_11.5±5.6 (Fs_49.1-61.0Wo_5.6-18.4, FeO/MnO = 32-33); High-Ca pyroxene (N=7): Fs_33.9±3.6Wo_37.9±4.2 (Fs_31.7-42.0Wo_28.6-40.6 FeO/MnO = 30-38); Plagioclase (n=13): An_87.9±0.2 (An_87.7-88.1).

Classification: Eucrite (monomict breccia), low weathering, moderate shock.

Specimens: 11.1 g and a polished thin section at ASU. Main mass with MFarmer