Northwest Africa 4816

Northwest Africa

Find: 2006

Achondrite (acapulcoite)

History and physical characteristics: A 63 g stone was purchased in Erfoud, Morocco, in 2006 by Stefan Ralew. The partial stone has moderate surface weathering of broken areas. Small metal spherules and droplets protrude through a thin, residual fusion crust.

Petrography: (T. Bunch and J. Wittke, NAU) Highly enriched in kamacite metal, mineral modes (in vol%) are orthopyroxene, 33; olivine, 25; kamacite, 24; diopside, 15, plagioclase and felsic glass, 3 and FeS + chromite, 1.0. Silicates are fine-grained (mean = 0.60 mm) and show euhedral to subhedral grain outlines. Orthopyroxene contains micrometer-sized glass blebs. Rare, round to ovoid granular clusters may represent relict chondrules. Shock level is S2 and the weathering grade is W1.

Mineral compositions: Olivine, Fa_5.6; FeO/MnO = 12. Orthopyroxene is Fs_6.2Wo_2.1, FeO/MnO = 9 and diopside is Fs_2.8Wo_45.5, FeO/MnO = 7. Plagioclase is An₆₆, chromite cr# = 69 and kamacite contains 6.1 wt% Ni. Felsic glass is (in wt%): SiO₂, 51.2; Al₂O₃, 20.3; CaO, 10.8; Na₂O, 2.6; K₂O, 0.8; MgO, 12.0 and FeO. 3.1.

Classification: Achondrite (acapulcoite).

Type specimen: A 12.4 g sample is on deposit at NAU. S. Ralew holds the main mass.