Deltoidal icositrahedron faceting on α-Fe crystals found on the surface of the Moon

K. M. Knowles and H. K. D. H. Bhadeshia

Abstract

Crystallographic analysis of scanning electron microscopy images of small μm-sized single crystals of b.c.c. iron found on the surface of the Moon shows that the deltoidal icositetrahedron faceting behaviour clearly seen is best describable as being from planes of the {229}_α; form. While possibly unexpected given the lack of any report of such faceting in terrestrial and meteoritic b.c.c. iron single crystals, this deltoidal icositetrahedron faceting behaviour can be rationalised straightforwardly in terms of the local chemical conditions which will have been experienced by these crystals while growing from the vapour in the part of the lunar environment from which these samples were obtained.

Journal of Crystal Growth 617(2023) 127257.

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Scanning electron micrograph of the contents of a fragmented rock from the Apollo 15 mission. The largest iron crystal resting in a cavity within the silicate rock, is about three micrometres in size. The perfection of the facets on these crystals indicates slow formation from hot vapour as the rock cooled. NASA image S72-55208, catalogued 10th November 1972.