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    Significance of opal in ureilites - delivery of H2O to the inner solar system?

    Beard, Andy and Downes, Hilary and Howard, K.T. (2011) Significance of opal in ureilites - delivery of H2O to the inner solar system? In: 74th Annual Meeting of the Meteoritical-Society, 2011, London, UK. (Unpublished)

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    Numerous fragments of opal (SiO2.nH2O) have previously been reported in 5 internal chips of polymict ureilite EET83309 [1]. The largest fragments are >300µm in the longest dimension and show clear banding. The bands are terminated by the adjacent olivine clasts, indicating that the opal clasts were not formed in situ. Opal is also found in contact with ureilitic olivine, forming a single clast with a terrestrial weathering rim around both minerals. It also occurs as thin (10µm) rims completely surrounding suessite (Fe3Si) grains, and can also contain inclusions of schreibersite. It shows no relationship whatsoever with terrestrial weathering rims. These petrographic observations indicate that the opal is (a) extraterrestrial in origin, and (b) native to the ureilite parent body. Suessite and schreibersite are considered to be the products of reduction during shock metamorphism. Therefore formation of the opal occurred after the formation of suessite but before the formation of the regolith represented by polymict ureilites.


    Item Type: Conference or Workshop Item (Paper)
    School: Birkbeck Faculties and Schools > Faculty of Science > School of Natural Sciences
    Depositing User: Sarah Hall
    Date Deposited: 10 May 2016 15:23
    Last Modified: 02 Aug 2023 17:23


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