Northwest Africa 12380 (NWA 12380)

(Northwest Africa)

Purchased: 2017

Classification: Ordinary chondrite (L3)

History: Specimen was purchased in Morocco in late 2017 by Brahim Tahiri and brought to Sean Tutorow before the 2018 Tucson Gem Show.

Physical characteristics: Physical Characteristics: Brownish and yellow-brown weathering patina occurs on rough exterior surfaces. Fractures filled with a yellow-white precipitate are visible cutting across the hand specimen. Interior is brown with crisply defined chondrules, and contains discreet light and dark colored clasts.

Petrography: (M. Hutson and A. Ruzicka, Cascadia) The host meteorite consists of sharply defined chondrules, chondrule fragments, and light-colored clasts up to 3 mm across set in a matrix comprised of angular fragments. Chondrules range in size from 0.14 to 2.5 mm, with a mean diameter of 0.74 mm (N=129). A single large (1 cm × 1 cm) dark clast that has a sharp contact with the host consists of well-defined chondrules (diameter 0.3-2.1 mm range, 0.83 mm mean, N=48) in an opaque matrix consisting of fine-grained material of differing texture and composition than the meteorite host. Two coarse-grained light colored clasts were examined in detail. One clast (approximately 2 × 3 mm in thin section) consists of a single large normally-zoned olivine grain approximately 2.5 mm long surrounded by smaller low-Ca pyroxene grains with high-Ca pyroxene overgrowths set in a feldspathic mesostasis. The other light-colored clast (approximately 1.3 × 1.5 mm in thin section) consists of coarse (up to 0.5 mm) twinned laths of low-Ca pyroxene poikilitically enclosing a few small olivine grains. In the meteorite roughly 80-90% of the opaque minerals have been replaced by Fe-hydroxides. A large vein of calcite cross-cuts the meteorite host but does not penetrate the dark clast.

Geochemistry: Mineral Compositions and Geochemistry: Olivine (host Fa_22.8±10.8, N=83; dark clast Fa_16.5±9.4, N=56; coarse olivine clast Fa_17.3±2.2, N=20), low-Ca pyroxene (host Fs_12.3±8.7Wo_1.1±1.1, N= 45; dark clast Fs_10.0±7.8Wo_1.2±1.4, N=31; coarse olivine clast Fs_17.3±2.2Wo_2.0±0.7, N=19; twinned pyroxene clast Fs_26.7±1.4Wo_1.5±0.5, N=10). Cr₂O₃ wt% in olivine (host 0.07±0.10, N=56; dark clast 0.14±0.08, N=40).

Classification: Ordinary chondrite L3. L group rather than LL based on chondrule diameter. Estimated subtype ~3.5 based on Fa statistics.

Specimens: Cascadia holds 21.4 g in two pieces, in addition to three polished thin sections and three mounted butts. Main mass held by Sean Tutorow.