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hibonite: crystal chemistry and origin of blue coloration in meteoritic assemblagesThe blue color and optical spectra of hibonite, a common constituent of refractory inclusions in carbonaceous chondrites, are discussed. Because they may be manifestations of exotic cation species stabilized in unusual coordination sites in the hibonite crystalstructure. Hibonite, ideally CaAl12O19, is conducive to atomic substitution of host Ca2+ and Al3+ ions by a variety of lanthanide and first series transition elements. The latter cations are responsible for the colors of many rock-forming minerals as a result of intraelectronic or intervalence transitions. The visible-region spectra of most oxide and silicate minerals are generally well understood. Assignments of absorption bands in meteoritic hibonite optical spectra due to uncertainties of cation valencies and complexities in the crystal structure are examined. The crystal chemistry of hibonite is reviewed, Mossbauer spectral measurements of iron-bearing hibonite and electronic transitions that may be responsible for the blue coloration of meteoritic hibonites are discussed.
Document ID
19850015244
Document Type
Other
Authors
Burns, R. G.
(Massachusetts Inst. of Tech. Cambridge, MA, United States)
Burns, V. M.
(Massachusetts Inst. of Tech. Cambridge, MA, United States)
Date Acquired
August 12, 2013
Publication Date
April 1, 1985
Publication Information
Publication: NASA, Washington Repts. of Planetary Geol. and Geophys. Program
Subject Category
INORGANIC AND PHYSICAL CHEMISTRY
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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