The origin of diamonds in ureilites is still a debated issue among the scientific community, with significant implications for the sizes of early Solar System bodies. We investigated three diamond-bearing ureilites by a multimethodological approach using scanning electron microscopy, micro X-ray diffraction, transmission electron microscopy, and micro-Raman spectroscopy, with the aim of determining the origin of the diamonds. Our results show that formation of both microdiamonds and nanodiamonds in ureilites can be explained by impact shock events on a small planetesimal and does not require long growth times at high static pressures within a Mercury- or Mars-sized body.

The origin of diamonds in ureilite meteorites is a timely topic in planetary geology as recent studies have proposed their formation at static pressures >20 GPa in a large planetary body, like diamonds formed deep within Earth’s mantle. We investigated fragments of three diamond-bearing ureilites (two from the Almahata Sitta polymict ureilite…