Northwest Africa 5718

Algeria

Purchased: 2006

Classification: Martian (basaltic shergottite)

History: A fresh, 90.5 g stone was purchased in Erfoud, Morocco, by Mr. Darryl Pitt in 2009. The stone is complete and covered with a shiny, lightly weathered fusion crust.

Petrography: (T. Bunch and J. Wittke, NAU; A. Irving, UWS):  This basaltic shergottite is fine to medium-grained (a few prismatic pigeonite grains reach 4.9 mm in length) with ophitic, subophitic, and granular textures. Pigeonite and augite account for 70 vol%, maskelynite (25 vol%), and ulvöspinel, ilmenite, pyrrhotite, and merrillite 5 vol%.  Pigeonite and augite are compositionally zoned with mottled extinction, shock lamellae, and kink bands. Small pockets of late-stage K-rich glasses with crystallites of ilmenite, merrillite, pyroxene, and silica are also present. Shock-formed dark, vesicular glass pockets and thin shock melt veins are prominent.

Geochemistry: Pigeonite cores, Fs _{30.5 - 39.1} Wo_9.6-11.5, rims, Fs _{41.8 - 45.7} Wo_12-13.2 (FeO/MnO = 32); augite Fs_{25.4 – 33.4}Wo_{28.3 – 31.1}, TiO₂ = 1.49 wt %  (FeO/MnO = 28). Plagioclase (maskelynite) is zoned with cores of An_56.8 Or_2.1 to rims of An_52.3 Or_4.8. Ilmenite MgO = 1.64 wt %.  K-rich glasses (wt %) SiO₂ = 77.1, Al₂O₃ = 11.6, K₂O = 7.1, Na₂O = 2.52, FeO = 1.45. Oxygen isotopes (D. Rumble, CIW): Replicate analyses of acid-washed whole rock samples by laser fluorination gave δ¹⁸O = 4.47, 4.29; δ¹⁷O = 2.60, 2.50; Δ¹⁷O = 0.253, 0.245‰. Bulk rare earth element abundances (ICPMS; C. Herd, UAb): La 3.49, Ce 8.57, Nd 5.92, Sm 2.27, Eu 0.83, Gd 3.63, Dy 4.35, Er 2.53, Yb 2.23, Lu 0.32 (all in ppm).

Classification: Martian (basaltic shergottite). This specimen is an "enriched" shergottite with REE abundances approximately 10 ×f chondrites.

Specimens: 19.4 g is on deposit at NAU*. DPitt is the main mass holder.