Northwest Africa 12455 (NWA 12455)

(Northwest Africa)

Purchased: 2018 Nov

Classification: Carbonaceous chondrite (CR7)

History: Purchased by Ben Hoefnagels in November 2018 from a dealer in Agadir, Morocco.

Petrography: (A. Irving and S. Kuehner, UWS; P. Carpenter, WUSL) This specimen has a triple grain junction texture (grainsize 0.3-1.5 mm) completely devoid of chondrules, and is composed of olivine, orthopyroxene, intermediate plagioclase, chromite, altered kamacite, taenite, troilite, pentlandite, and minor secondary calcite. Modal metal content is ~5 vol.%; troilite is much less abundant, as small blebs, ~0.5 vol.%.

Geochemistry: Olivine (Fa_35.0-35.3, FeO/MnO = 83-94, N = 4), orthopyroxene (Fs_27.8-28.0Wo_3.5-4.0, FeO/MnO = 51-56, N = 4), plagioclase (An_48.2-48.9Or_1.1, N = 2), kamacite (Ni = 7.2 wt.%), taenite (Ni = 16.4 wt.%). Oxygen isotopes (K. Ziegler, UNM): analysis of acid-washed subsamples by laser fluorination gave, respectively: δ¹⁷O 0.661, 0.470, 0.296, 0.359, 0.375, 0.303; δ¹⁸O 4.314, 4.021, 3.637, 3.840, 3.939, 3.761; Δ¹⁷O -1.617, -1.653, -1.625, -1.668, -1.705, -1.683 per mil. Chromium isotopes (M. Sanborn and Q. Yin, UCD): 54Cr is the same within analytical uncertainty as that for CR2 chondrite Renazzo reported by Sanborn et al. (2019).

Classification: Carbonaceous chondrite (CR7). This specimen exhibits a completely recrystallized texture with no evidence of remnant chondrules, and has oxygen isotopic compositions which plot on the established trend for CR chondrites.

Specimens: 22.3 g including two polished thin sections at UWB; remainder with Mr. B. Hoefnagels.