Detailed 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} form. While possibly unexpected given the lack of any report of such faceting in terrestrial and meteoritic b.c.c. iron single crystals, this ‘unusual’ 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.

Figure caption: (a) Part of NASA image S72-55208 from the Apollo 15 mission to the Moon. Three iron crystals with {100} faceting and {hhl} deltoidal icositetrahedral faceting are evident in this scanning electron microscope image. (b) – (d) Idealised orthographic projectional geometry of the three crystals assuming that the {hhl} facets are {229}.