Sayh al Uhaymir 169

Oman

Found 2002 January 16

Lunar meteorite (KREEP-rich mafic impact melt breccia and adhering regolith)

A complete, light grey-greenish rounded stone (70 × 43 × 40 mm) weighing 206.45 g was found in the Sayh al Uhaymir region of Oman. Finders, mineralogy and classification: E. Gnos, B. A. Hofmann, and A. Al-Kathiri (UniBern): dark brown fusion crust is only locally preserved. The impact melt breccia (87 vol% of the stone, based on 8 X-ray tomographic sections) contains 25–40 vol% of strongly shocked igneous rocks and crystal clasts (up to 17 mm) derived from norites, evolved magmatites, and granulites set in a fine-grained (<0.1 mm) crystalline matrix. Most crystal fragments are shocked plagioclases, locally associated with enstatite. In addition to plagioclase metallic iron, spinel, olivine, and orthopyroxene clasts are present. The fine-grained impact melt matrix consists mainly of short prismatic low-Ca pyroxene (En61–64, Wo2–4), interstitial plagioclase (An75–81) intergrown with potassium feldspar. The remaining minerals are poikilitic ilmenite, whitlockite, olivine (Fo58–59), zircon, and traces of troilite, kamacite and tridymite. The regolith (13 vol%) present one one side of the meteorite comprises crystalline and glassy volcanic rocks, igneous lithic fragments, breccia fragments, fragments of mafic granulites, and crystal fragments. The impact melt breccia contains 32 ppm Th and 8.5 ppm U, 0.47% K (K/U = 553), indicating a lunar origin.This is further confirmed by fusion-crust Fe/Mn of 75.1 (microprobe, n = 14) and impact melt bulk Fe/Mn of 79. Oxygen isotope composition (I. A. Franchi, OU) are also consistent with a lunar origin (∆¹⁷O = 0.001 ± 0.032‰). This impact melt breccia is the most strongly KREEP-eriched lithology among all known lunar rocks. Weathering: W1 (Fe metal shows only little oxidation). Specimens: All in NMB.