Northwest Africa 6454 (NWA 6454)

(Northwest Africa)

Purchased: February, 2005

Classification: Ordinary chondrite (L, melt rock)

History: In February 2005, Mr. Blaine Reed sold a portion of the sample to Mr. Turecki and that same year pieces were acquired by Cascadia from both Mr. Reed and Mr. Turecki.

Physical characteristics: The single stone is largely covered by a shiny black fusion crust that appears to be relatively unweathered.

Petrography: (A. Ruzicka and Melinda Hutson, Cascadia): The meteorite lacks chondritic texture and is dominated by fine-grained (<20 μm) euhedral to subhedral olivine set in glass. Metal and sulfide (~5-10% of sample) form cellular and dendritic intergrowths in composite particles up to a few millimeters across. Silicate portions can be subdivided into coarser, clast-like portions (olivine grain size 5-15 μm across) and finer-grained interstitial areas (olivine grains <3 μm across). Shock veins connect some of the metal-sulfide particles and in places merge into the finer-grained silicate regions. Clasts of olivine and low-Ca pyroxene are present which show a recrystallization texture (granular subgrains meeting in triple junctions).

Geochemistry: (K. Hauver and A. Ruzicka, Cascadia) Metal consists of kamacite with Ni = 6.12 ± 1.54 wt% and Co = 0.84 ± 0.06 wt% (N=7); martensite with Ni = 12.8 ± 2.9 wt% and Co = 0.77 ± 0.10 wt% (N=51), taenite with Ni = 27.7 ± 6.8 wt% and Co = 0.61 ± 0.11 wt% (N=12), and tetrataenite. Sulfide dominated by troilite with a minor Cr-sulfide phase.

Classification: Ordinary chondrite melt rock (shock melt). Textures of silicate and metal-sulfide particles suggest rapid cooling from a melt and the presence of shock-recrystallized xenocrysts. Kamacite Co contents fall within the range of L chondrites and the overall metal + sulfide content is consistent with this type of protolith.

Specimens: Type specimens available at Cascadia include 4 pieces totaling 20.0 g, plus one polished thin section and one polished potted butt. Turecki holds the main mass.