Northwest Africa 6580 (NWA 6580)

(Northwest Africa)

Purchased: October, 2005

Classification: Ordinary chondrite (L, melt breccia)

History: A portion of the sample was donated to Cascadia on December 13, 2005

Physical characteristics: The single stone is largely covered by a brown-black fusion crust that has prominent shrinkage cracks.

Petrography: (A.Ruzicka and K. Hauver, Cascadia) The main lithology is nearly devoid of opaque minerals and consists largely of fine-grained (~50-100 μm) euhedral to subhedral olivine set in glass; this lithology is in sharp contact with a small area (~9 mm) at the edge of the stone that shows chondritic texture.

Geochemistry: Mineral compositions and geochemistry: Fine-grained portion has olivine Fa _18.8±6.9 (n=11); chondritic portion has olivine Fa _22.8±3.4, median 24.1 (n=24); kamacite Ni 4.78±1.55 wt% and Co 0.89±0.14 wt% (n=19); martensite Ni 13.4±4.3 wt% and Co 0.64±0.13 wt% (n=12).

Classification: Ordinary chondrite melt-breccia. Olivine Fa and kamacite Co contents from the chondritic portion are similar to L chondrites, and martensite composition is similar to the bulk composition of metal in L chondrites.

Specimens: Type specimens available at Cascadia include 1 piece originally 20.0 g, from which one polished thin section and one polished butt were made. Thompson holds the main mass.