NWA 4222 meteorite, Erfoud (Erfud), Er Rachidia Province, Meknès-Tafilalet Region, Morocco

Northwest Africa 4222
Northwest Africa
Find: 2006
Martian (shergottite)
History: A small fragment was purchased in Erfoud
by a Moroccan dealer for M. Chinellato.
Physical characteristics: The sample weighs 16.5 g
and is partially covered with a black fusion crust.
Petrography (V. Moggi Cecchi, G.Pratesi, MSP):
Cumulitic fine-grained porphyritic texture consisting
of few very large rounded and zoned phenocrysts of
brown olivine up to 1350 μm in maximum size set in a
fine-grained basaltic groundmass of twinned tabular
pyroxene crystals from 80 to 240 μm wide and from
130 to 820 μm long surrounded by an interstitial
glassy matrix. Pyroxene is primarily pigeonite with
subordinate enstatite. Other minerals are chromite,
titanian chromite and ilmenite, up to 100 μm in size,
merrillite, and rare pyrrhotite grains up to 50 μm in
size; shock features include strong mosaicism and
planar deformation in olivine, undulose extinction and
twinning in pyroxene.
Geochemistry: Mineralogy: Olivine Fo58.9-68.7;
orthopyroxene (core Fs17.2En80.3Wo2.4; rim
Fs31.4En63.9Wo4.7, FeO/MnO = 30.2-42.4); pigeonite
(core Fs24.1En65.5Wo10.3; rim Fs32.6En58.4Wo8.9),
FeO/MnO = 32.5-46.5). Plagioclase (An61.1Or0.2).
Oxygen isotopes (I.A. Franchi, R. Greenwood, OU):
δ17O = 2.85 ‰, δ18O = 4.91 ‰, Δ17O = 0.30 ‰ (mean
on 2 analyses).
Classification: Martian (shergottite) Low weathering
and high shock.
Type specimens: A total of 3.55 g of sample and one
thin section is on deposit at MSP. Chin holds the main
mass.