THE OLD WOMAN, CALIFORNIA, METEORITE. C. M. Corrigan1, R. S. Clarke, Jr.1, H
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74th Annual Meteoritical Society Meeting (2011) 5450.pdf THE OLD WOMAN, CALIFORNIA, METEORITE. C. M. Corrigan1, R. S. Clarke, Jr.1, H. Plotkin2, and T. J. McCoy1. 1Smithsonian Institution, NMNH, P.O. Box 37012, Washington, DC, 20013-7012. E-mail: [email protected]. 2University of Western Ontario, London, ON. Introduction: The Old Woman meteorite, discovered in March, 1976, by two prospectors searching for a fabled lost Spanish gold mine in mountains ~270 km east of Los Angeles, achieved legendary status among meteorite collectors. History of the Old Woman Meteorite: The question of the ownership of the meteorite gave rise to four years of disputes. Ultimately, ownership of the meteorite was transferred to the Smithsonian under the powers of the 1906 Antiquities Act, a rul- ing upheld in a U.S. District Court and a U.S. Court of Appeals. After additional debate, the Smithsonian removed a 0.5 m2 cut for study and curation, and for disbursement of specimens to quali- fied researchers. The main mass was then returned to California on long-term loan to the Bureau of Land Management way sta- tion in Barstow. The Old Woman meteorite litigation served as an important test case for the ownership and control of meteorites found on federal lands. Scientific importance of the Old Woman Meteorite: The Old Woman meteorite, a 2753 kg group IIAB meteorite, is the second largest meteorite (~0.8 x 0.9 x 1.0 m) ever found in the United States. The large slice retained at the Smithsonian reveals distinct regions that show the transition between hexahedral IIA and octahedral IIB iron meteorite structures, a greater under- standing of the solid-state transformation that occurs during cool- ing. The slice is comprised of a polycrystalline mass with grain sizes ranging from <1 cm to > 40 cm in maximum dimension, with a strongly bimodal distribution. At high temperature, each grain was an independently oriented austenite crystal. Seven large grains comprise ~85% of the surface area and comprise the hexahedral structure within the meteorite, with the remaining 15% of the surface sampling the octahedral polycrystalline re- gions up to 20 cm in maximum dimension with grain sizes of 1-3 cm. More rarely, smaller grains are found completely enclosed (at least in two-dimensions) within the larger grains. Within the larger grains (hexahedrite, Region 1), kamacite is the only Fe,Ni metallic phase identified. Taenite was not seen. Numerous schreibersite grains up to several cm in length suggest remnant Widmanstätten, similar to Zacatecas [1]. Shock-melted sulfide inclusions contain troilite and daubreelite. Within Region 2, which might be called a coarsest octahedrite in isolation, smaller parent austenite grains are converted completely to kamacite and lack any remnant Widmanstätten pattern [2]. Thin ribbons of schreibersite and sulfides are seen. Traverses across schreibersites yield identical compositions of unzoned schreiber- site in both remnant Widmanstatten pattern of the hexahedral structure in Region 1, and at kamacite-kamacite grain boundaries in Region 2. If sampled separately, the individual lithologies of Old Woman might well have been classified as three distinct meteor- ites. Instead, we now recognize that transitional textural types do occur in close proximity and can provide clues to unravelling the unique combinations of chemistry and nucleation and cooling history [3] that produce these textures. References: [1] Buchwald V. 1975. Zacatecas (1792), in Handbook of Meteorites. Berkeley and Los Angeles: U of CA Press, 3: 1361. [2] Clarke R. S., Jr. 1979/2011, pers. comm.. [3] Yang and Goldstein, 2005, MAPS 40, 239. .