||NWA 4590 (Tamassint)
||Found 2006, Algeria
||Polished thin section
History: Scattered fragments from a small stone which appears to have shattered upon landing
recently were recovered from an area of ~40 m2 in the Morocco-Algeria border zone, 21 km
SSW of Tamassint oasis and 18 km S of Agoult, Morocco. G. Hupé purchased all the
recovered material in June 2006 in Tagounite, Morocco. He then traveled to Tamassint and
was shown the location by the original find and measured GPS coordinates.
Physical characteristics: Fragments totaling 212.8 g of a very friable specimen composed of
coarse yellow-green, black and white grains; very fresh with preserved shiny, black fusion crust
on some pieces, and minor pale orange terrestrial weathering coatings on some broken
Petrography: (A. Irving and S. Kuehner, UWS) Coarse grained (mostly 0.6-1.6 mm, but some
olivine grains up to 12 mm) with a cumulate texture and composed of clinopyroxene (33 vol%,
with rare pigeonite exsolution lamellae), pure anorthite (28 vol%), olivine (14 vol%, with
prominent subparallel exsolution lamellae (10-50 microns wide) of kirschsteinite),
kirschsteinite (5 vol%, with thin exsolution lamellae of olivine), ulvöspinel (18 vol%), and
accessory glass, troilite, merrillite, Ca-silicophosphate and kamacite (making up the
remaining 5 vol%). Some anorthite occurs as subhedral grains partially enclosed within large
ulvöspinel grains, but most occurs as intercumulus aggregates. Clinopyroxene is strongly
zoned with paler colored, corroded cores surrounded by darker purple-brown mantles and
distinct rims. Thin (5-50 µm wide) discontinuous, curvilinear zones of glass are present on
some grain boundaries (notably those between anorthite and ulvöspinel, but also around and
cutting across troilite grains), and are associated with secondary clinopyroxene, kirschsteinite,
olivine, anorthite and troilite grains; these films of glass+daughter minerals truncate
kirschteinite exsolution lamellae in adjacent olivine. This angrite is unlike other known
specimens, having neither a fine-grained quench or ophitic/intesertal basaltic texture nor a
coarse metamorphic texture.
Mineral compositions and geochemistry: Clinopyroxene (Fs20.8-33.3Wo53-54.9; FeO/MnO =
85-278), olivine host (Fa72.6-74.7Ln3.5-3.6; FeO/MnO = 70-87), kirschsteinite lamellae (Fa44.
7-45.4Ln46-47.2; FeO/MnO = 73-82), kirschsteinite host (Fa46.6-47.5Ln43.6-45.5; FeO/MnO
= 63-68), olivine lamellae (Fa75-76.7Ln2.7-2.8; FeO/MnO = 71-74). Oxygen Isotopes: (D.
Rumble, CIW) Analyses of two aliquots of acid-washed mineral fragments by laser fluorination
gave, δ18O = 3.845, 3.881; δ17O = 1.927, 1.967; Δ17O = 0.0956, 0.0745 (all ‰).