LINK<\/strong><\/a><\/p>\n“The Al-rich oxide hibonite (CaAl12O19) is modelled to be the second mineral to condense from a gas of solar composition and is found within calcium-aluminum-rich inclusions and the matrix of chondritic meteorites. Both Ti3+ and Ti4+ are reported in meteoritic hibonite, so hibonite has been proposed as a single mineral oxybarometer that could be used to elucidate conditions within the first 0.2 Myrs of the Solar System.
\nSynthetic hibonites with Ti3+\/(Ti3++Ti4+) (hereafter Ti3+\/\u03a3Ti) ranging between 0 and 1 were prepared as matrix-matched standards for meteoritic hibonite. The largest yield of both Ti-free and Ti-bearing hibonite at \u223c1300 and \u223c1400 \u00b0C was obtained by a single sinter under reducing conditions.
\nIn situ micro-beam Ti K-edge X-ray absorption near edge structure (XANES) spectra were collected from the synthetic hibonites, as well as from terrestrial hibonite. Spectral features in the post-crest region were shown to correlate with the Ti4+ content. Furthermore, Ti4+ on the M2 trigonal bipyramidal and the adjoining M4 octahedral sites appears to cause variability in the post-crest region as a function of orientation. For this suite of synthetic hibonites it was observed that the pre-edge peak region is not influenced by orientation, but is controlled by Ti3+\/\u03a3Ti, site geometry and\/or Ti concentration. In particular, the pre-edge peak intensities reflect Ti coordination environment and distortion of the M4 octahedral site. Therefore, although pre-edge peak intensities have previously been used to determine Ti3+\/\u03a3Ti in meteoritic minerals, we excluded use of the pre-edge peak intensities for quantifying Ti valence states in hibonite.
\nThe energy of the absorption edge at a normalized intensity of 0.8 (E0.8) and the energy of the minimum between the pre-edge region and the absorption edge (Em1) were found to vary systematically with Ti3+\/\u03a3Ti. Ti3+\/\u03a3Ti in hibonite as a function of Em1 was modelled by a quadratic function that may be used to quantify Ti3+\/\u03a3Ti in meteoritic hibonite when the synthetic hibonite standards are crystal-chemically matched to the natural samples and are measured during the same analytical session as the meteoritic hibonites.”<\/p>\n","protected":false},"excerpt":{"rendered":"
P.M. Doyle, A.J. Berry, P.F. Schofield, J.F.W. Mosselmans Geochimica et Cosmochimica Acta In Press, Accepted Manuscript, Available online 12 May 2016 LINK “The Al-rich oxide hibonite (CaAl12O19) is modelled to be the second mineral to…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[66,58,57],"tags":[2822,2823],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/8699"}],"collection":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=8699"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/8699\/revisions"}],"predecessor-version":[{"id":8700,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/8699\/revisions\/8700"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=8699"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=8699"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=8699"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}