Northwest Africa 10593 (NWA 10593)

Morocco

Purchased: 2014 Sept

Classification: Martian meteorite (Shergottite)

History: Purchased by D. DGregory at the Denver mineral show in September 2014 from a Moroccan dealer

Physical characteristics: (I. Nicklin, ROM) Two pieces with an aggregate weight of 279.0 g, the largest piece weighs 219.0 g. Notably regmaglypted surface with significant (~50%) remnant fusion crust, although some of what appears to be fusion crust is actually melt glass showing through from the interior of the specimen. A small amount of caliche is present on one surface. Where the fusion crust is absent, the interior contains small, randomly oriented, gray-green pyroxene grains surrounding transparent grains of plagioclase.

Petrography: Petrograph: (I. Nicklin, ROM) In thin section, the rock is composed of medium-grained prismatic pyroxenes up to 2.5 mm in length intermixed with more equant pyroxene grains in the 1 mm range. The prismatic pyroxenes show twinning. The pyroxenes generally surround stubby to lath-shaped grains of isotropic plagioclase-composition glass based on EMP analysis. In crossed polars, this glass shows crystallites of sub-radiating, gray-white anisotropic needles arranged in margins where the glass is in contact with pyroxene grains. Another notable feature is the presence of large areas (~25% of the cut surface area) of dark-colored, interconnecting melt-glass pockets with vesicles up to or exceeding 1 mm in greatest dimension. In addition to the melt-glass pockets, vesicles and plagioclase-composition glass there are pervasive planar fractures especially noticeable in the prismatic pyroxenes and mosaicism plainly apparent in all the pyroxene grains. No olivine has been observed.

Geochemistry: Mineral compositions and geochemistry: (V. Di Cecco, ROM) Pyroxenes: chaotically zoned augite cores (Fs_27.6±7.8Wo_30.6±1.8 (n=11); FeO/MnO = 30.8±3.6 (n=11)) ferropigeonite rims (Fs_61.4±7.4Wo_17.1±2.8 (n=7) ; FeO/MnO = 38.4±1.2 (n=7)) and pigeonite mantles (Fs_39.2±8.0Wo_13.6±1.9 (n=11); FeO/MnO = 32.2. The average composition of the plagioclase is An_48.3±4.7Or_2.85±1.7 (n=19). Oxygen isotopes (K. Ziegler, UNM): analyses of four acid-washed subsamples by laser fluorination gave, respectively, δ¹⁷O = 2.576, 2.736, 2.710, 2.582; δ¹⁸O 4.373, 4.714, 4.691, 4.484; Δ¹⁷O = 0.267, 0.247, 0.233, 0.214 (all values in per mil).

Classification: Martian (shergottite)

Specimens: 20.5 g plus one polished thin section are on hand at the ROM and constitute type material. The remainder is held by DGregory.