Northwest Africa 13088 (NWA 13088)

Morocco

Purchased: 2017

Classification: Ordinary chondrite (L3.1)

History: Purchased in Morocco by Brahim Tahiri in late 2017 and brought to Sean Tutorow in late December 2017. Tutorow donated 94.40 g to Cascadia for classification.

Physical characteristics: Cascadia received two thin slices completely covered in a coating which darkens the sample and causes it to appear wet. Overall, the slices are dark orange-brown in color and show abundant chondrules. Some areas have chondrules set in an orange-brown background, while in other areas the background is dark brown to black. Boundaries between the two are generally indistinct, although there is one example of a sharp contact between a large (4 × 3 cm, truncated along the edge of the slice), angular, orange-brown colored clast and the rest of the slice, indicating that this sample is brecciated.

Petrography: (M. Hutson and A. Ruzicka, Cascadia): The section is crossed by numerous weathering veins composed of calcite and iron-rich hydroxides. One edge of the section is less weathered and shows abundant discolored and partially-replaced troilite, much of it as rims around chondrules. Chondrules are distinct, and have an apparent mean diameter of 756±366 microns (N= 113). Two subtly different lithologies with indistinct boundaries are visible in thin section in optical and BSE imaging. One lithology (lithology A) has a somewhat higher proportion of forsteritic olivine grains than the other (lithology B); the overall lithology A clast appears slightly darker in BSE imaging. Chondrule mesostases in lithology A contain fewer crystallites than those of lithology B.

Geochemistry: Mineral compositions and geochemistry: Olivine and pyroxene grains are highly unequilibrated: Fa_17.7±10.7N=161; Fs_11.5±10.1Wo_1.0±1.1, N=82. There is no significant difference in Fa or Fs contents between the two lithologies. However, Cr₂O₃ in olivine suggests a slightly different petrographic subtype: Cr₂O₃ in olivine (lithology A) = 0.42±0.19 wt%, consistent with a subtype of 3.10, N=72; Cr₂O₃ in olivine (lithology B) = 0.19±0.21 wt%, consistent with a subtype of 3.15, N=84.

Classification: Ordinary chondrite (L3.1) based on olivine fayalite content, overall Cr₂O₃ in olivine, and mean chondrule diameter.

Specimens: Cascadia holds 90.3 g in six pieces, in addition to a polished thin section and a mounted butt. The main mass is held by Sean Tutorow, Arizona.