Northwest Africa 8709 (NWA 8709)

(Northwest Africa)

Purchased: 2003 Nov 23

Classification: Ordinary chondrite (L3, melt breccia)

History: An already cut individual of an NWA meteorite was purchased by Dick Pugh in November 2003 and May 2004 from a Portland, Oregon, vendor and donated to Cascadia.

Physical characteristics: An irregularly shaped specimen with a dark, bumpy exterior, which locally has remnant fusion crust and a reddish brown weathering patina. Cut faces are dark gray and show distinct chondrules.

Petrography: (M. Hutson and A. Ruzicka, Cascadia) Tightly packed and commonly ellipsoidal chondrules in thin section (mean diameters in two thin sections are 0.72±0.36 mm, N=30; and 1.0±0.4 mm, N=23) with long axes roughly aligned, are embedded in an igneous-textured matrix composed of fine-grained (<5-10 μm) olivine, low-Ca pyroxene, glass, Ca-pyroxene, sulfide, and metal (or weathered metal), with sulfide and metal sometimes forming larger globules (to 40 μm). Chondrules consist chiefly of olivine and low-Ca pyroxene containing many small sulfide or metal inclusions and veinlets, set in glass or fine grained mesostasis. Olivine grains in chondrules show undulose-mosaic extinction and planar fractures consistent with shock stage S4. 80-90% of opaque minerals are replaced by terrestrial weathering products. Weathering products and remaining metal and troilite constitute ~5 area % (visual estimate) of the coarser grains in thin sections. No clasts of different chondrite types are apparent.

Geochemistry: Olivine Fa_15.6±2.9 (Fa_2.1-20.8, N=99) and low-Ca pyroxene Fs _11.1±5.2Wo_1.5±1.4 (Fs_2.2-21.7, N=39) in chondrules. Oxygen isotopic composition (R. Greenwood, OU) of untreated bulk sample, δ¹⁷O 3.482, δ¹⁸O 5.033, Δ¹⁷O 0.865 (0.842 linearized), all permil.

Classification: Based on texture and mineral chemistry this stone is a type 3 chondritic melt breccia. Group affinity is likely L chondrite based on oxygen isotope composition (most consistent with L chondrite), chondrule size (consistent with L or LL chondrite), and overall amount of metal and sulfide and associated weathering products (consistent with L or LL chondrite). Mineral chemistry is not fully consistent with established chondrite groups and most closely resembles H chondrites.

Specimens: 70.8 g as well as polished thin section are on deposit at Cascadia, which holds the main mass. The original specimen is estimated to have been at least 79 g.