Beckettite, Ca2V6Al6O20, a new mineral in a Type A refractory inclusion from Allende and clues to processes in the early solar system

1Chi Ma,2Alexander N. Krot,1Julie Paque,3Oliver Tschauner,1Kazuhide Nagashima
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13771]
1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, 91125 USA
2Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i, 96822 USA
3Department of Geoscience, University of Nevada, Las Vegas, Nevada, 89154 USA
Published by arrangement with John Wiley & Sons

Beckettite (Ca2V6Al6O20; IMA 2015-001) is a newly discovered refractory mineral, occurring as micrometer-sized grains intergrown with hibonite and perovskite, and surrounded by secondary grossular, anorthite, coulsonite, hercynite, and corundum. It occurs within highly altered areas in a V-rich, Type A Ca-Al-rich inclusion (CAI), A-WP1, from the Allende CV3 carbonaceous chondrite. The type beckettite has an empirical formula of (Ca1.99Na0.01)(V3+3.47Al1.40Ti4+0.57Mg0.25Sc0.08Fe2+0.04)(Al5.72Si0.28)O20, with a triclinic structure in space group Purn:x-wiley:10869379:media:maps13771:maps13771-math-0001 and cell parameters a = 10.367 Å, b = 10.756 Å, c = 8.895 Å, α = 106.0°, β = 96.0°, γ = 124.7°, V = 739.7 Å3, and Z = 2, which leads to a calculated density of 3.67 g cm−3. Beckettite’s general formula is Ca2(V,Al,Ti,Mg)6Al6O20 and the endmember formula is Ca2V6Al6O20. Beckettite is slightly 16O-depleted (Δ17O = −16 ± 2‰) compared to the coexisting hibonite and spinel −24 ± 2‰. Beckettite is a primary high-temperature mineral resulting from igneous crystallization of an 16O-rich V-rich CAI melt together with V-bearing hibonite, perovskite, burnettite, spinel, and paqueite. Subsequently, beckettite experienced an incomplete isotope exchange with an 16O-poor aqueous fluid (Δ17O = −3 ± 2‰) on the Allende parent asteroid.

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