Northwest Africa 2405 (NWA 2405)

(Northwest Africa)

Purchased: Jan 2018

Classification: HED achondrite (Eucrite, brecciated)

History: The meteorite was exported from Morocco to Tucson where it was purchased by N. Gessler.

Physical characteristics: 20% fusion crusted. The interior displays a distinctive structure of angular pale tan clasts of basalt (3/4) set in a subordinate proportion (1/4) of dark grey, vein-like (shock-melted) materials, with vein widths ranging from indiscerniblly thin to approximately, locally, 3 mm.

Petrography: The rock consists predominantly of clasts of little-brecciated subophitic basalt, with grain sizes generally near 1 mm, with a typical pyroxene and plagioclase dominated eucritic mode, and displaying typical eucritic thermal-metamorphic exsolution in pyroxene. The shock state of the clastic matter varies; locally, its plagioclase has been partially maskelynitized. The subordinate component of shock-melt vein material that choaotically criss-crosses the rock is much finer grained.

Geochemistry: Low-Ca pyroxene clusters near Fs₆₁Wo₂, augite near Fs₂₇Wo₄₃, both typical for a noncumulate eucrite. Pyroxene FeO/MnO averages (26 analyses) 31.5. Plagioclase (8 analyses) is An_88-90. The bulk composition, determined by INAA and fused-bead EPMA applied to 2 chips totaling 650 mg, is fairly nondescript for a eucrite, with bulk Mg/(Mg+Fe) ~ 38 mol%, 0.6 wt% TiO₂, and 0.44 wt% Na₂O; and shows little difference between a chip dominated (~70%) by dark shock-vein matter and a chip of preponderantly (~95%) pale tan clastic matter.

Classification: Eucrite, brecciated.

Specimens: Main mass with Gessler, type specimen at UCLA.