Northwest Africa 2748

Northwest Africa

Find: February 2002

Ordinary chondrite (LL3.4)

History: A single stone was purchased in February 2002 from a trader in Erfoud, Morocco, by R. Elliott.

Physical characteristics: The 57 g stone is partly covered in dark brown fusion crust. Patches of limonitic surface coating are present, from which irregular veins penetrate the interior. Abundant large chondrules are visible to the unaided eye.

Petrography: (R. Hutchison and A. Kearsley, NHM; P. Sipiera, Harper) Chondrules constitute >80% of the stone and range up to >4 mm in size. The mean apparent size of 183 chondrules is 0.89 ± 0.48 mm. The chondrules have sharply defined margins and many are mutually indented, resembling compound chondrules. PO and POP chondrules dominate. A 1.3 mm spinel-pyroxene CAI was identified. Zoning is common at chondrule margins. Little metal has survived terrestrial alteration but some kamacite and taenite are present.

Mineral compositions and geochemistry: In chondrules, the minimum range of olivine cores is Fo_99–65. One analysis of matrix yielded Mg/(Mg + Fe) = 32. A 4 mm PO chondrule fragment has zoned olivines whose cores are Fo₈₅ with Ni = 0.74 wt%. A type IA PO chondrule has olivines (Fo_99–97) with CaO = 0.6–0.9 wt%. Oxygen isotopes: (R. C. Greenwood, OU) δ¹⁷O = 4.870, 4.914; δ¹⁸O = 7.176, 7.242; Δ¹⁷O = +1.138, +1.148 (all ‰, the second values are replicates).

Classification: Ordinary chondrite (LL3.4 ± 0.2).

Type specimen: A 10.86 g part-slice (BM 2004, M.6) and one thin section are in NHM. A 3 g sample and one thin section are held by DuPont. A 5.15 g slice is with R. Hutchison, NHM. Fernlea holds the main mass.