Old Woman Meteorite: microstructures, analyses, and stories

Abstract The Old Woman Meteorite (OWM), the second largest found in the USA, was located by prospectors in a steep canyon in the Mojave Desert about 20 km south of Highway 66 in March of 1976. Because of its weight of nearly 3 metric tons it had to be airlifted out of the mountains by a US Marine helicopter. A small triangular metallographic sample, on loan from the University of California Los Angeles, UCLA, was examined by light microscopy and energy dispersive X-ray spectroscopy (EDS) analysis to identify the structures and phases present. Rhabdites and schreibersite are visible in the as-polished condition. Nital etchant reveals grain boundaries and Neumann bands. Etching with Klemm I colors kamacite grains(ferrite) and Neumann bands in shades of blue and brown according to the crystal orientation. Prism shaped rhabdites stay white. Many rhabdites show cracks at the intersection with Neumann bands. Three areas with unusual structures were found. EDS dot maps identified one as schreibersite, another area contains troilite, schreibersite, brezinaite and possibly taenite, the third location contains Fe, Ni, P and S.