Chi Ma¹ and Alexander N. Krot²

¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
²Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Mänoa, Honolulu, Hawai’i 96822, U.S.A.

Hutcheonite (IMA 2013-029), Ca₃Ti₂(SiAl₂)O₁₂, is a new garnet mineral that occurs with monticellite, grossular, and wadalite in secondary alteration areas along some cracks between primary melilite, spinel, and Ti,Al-diopside in a Type B1 Fractionation and Unidentified Nuclear effects (FUN) Ca-Al-rich inclusion (CAI) Egg-3 from the Allende CV (Vigarano type) carbonaceous chondrite. The mean chemical composition of type hutcheonite by electron probe microanalysis is (wt%) CaO 34.6, TiO₂ 25.3, SiO₂ 20.9, Al₂O₃ 15.7, MgO 2.1, FeO 0.7, V₂O₃ 0.5, total 99.8, giving rise to an empirical formula of Ca_2.99(Ti⁴⁺_1.53Mg_0.25Al_0.17Fe²⁺_0.05V³⁺_0.03)(Si_1.68Al_1.32)O₁₂. The end-member formula is Ca₃Ti₂(SiAl₂)O₁₂. Hutcheonite has the Ia3̄d garnet structure with a = 11.843 Å, V = 1661.06 ų, and Z = 8, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 3.86 g/cm³. Hutcheonite is a new secondary phase in Allende, apparently formed by iron-alkali-halogen metasomatic alteration of the primary CAI phases like melilite, perovskite, and Ti,Al-diopside on the CV chondrite parent asteroid. Formation of the secondary Ti-rich minerals like hutcheonite during the metasomatic alteration of the Allende CAIs suggests some mobility of Ti during the alteration. The mineral name is in honor of Ian D. Hutcheon, a cosmochemist at Lawrence Livermore National Laboratory, California, U.S.A.

Reference
Ma C and Krot AN (2014) Hutcheonite, Ca3Ti2(SiAl2)O12, a new garnet mineral from the Allende meteorite: An alteration phase in a Ca-Al-rich inclusion. American Mineralogist 99:667.
[doi:10.2138/am.2014.4761]
Copyright: The Mineralogical Society of America

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