Seminario - Asteroid impact-formed complex diamond structures

Relatore: Prof. Péter Németh - Institute for Geological and Geochemical Research, HUN-REN Research Centre for Astronomy and Earth Sciences (Hungary) | Martedì 5 Maggio 2026 | ore 16,30 - Aula Arduino

05.05.2026

Around 50,000 years ago an ~60 m metal asteroid traveling at 11 km/s impacted on the flat plains of northern Arizona (USA) creating the 200 m deep and 1.2 km diameter Meteor Crater (also called Barringer Crater). The impact, estimated to correspond to 10 megatons of TNT and generated an intense shockwave affecting both the impacted country rocks as well as surviving pieces of the asteroid called the Canyon Diablo iron meteorite. In 1967, scientists investigating fragments of the meteorite announced the discovery of a new form of diamond, which they speculated to have been formed in the extreme impact conditions.
Terrestrial diamonds have cubic symmetry, but these ones had hexagonal symmetry. The new material was named lonsdaleite after the pioneering British crystallographer, Professor Dame Kathleen Lonsdale. Since then, lonsdaleite has been reportedly found in several other meteorites and has been associated with asteroid impacts. Scientists also speculated that the hexagonal diamond could possess properties superior to that of cubic diamond, stimulating attempts to synthesize pure lonsdaleite.
In my presentation, I demonstrate the ultra-high-resolution transmission electron microscopy and X-ray diffraction analysis of the hard carbon grains, originally identified as lonsdaleite, from Canyon Diablo meteorite. I will show that lonsdaleite is not hexagonal diamond but a nanocomposite consisting of cubic/hexagonally stacked diamond and their association with crystallographically intergrown diamondgraphite units, called diaphites (Fig. 1). I will further show that the carbonaceous materials from Gujba, Orgueil and Murchison meteorites reveal similarly complex structures. The complexity found in these sample can occur in a wide range of carbonaceous materials produced by shock and static compression or by deposition from a vapour. The recognition of the various graphene and diamond stackings is relevant for understanding the pressure-temperature conditions that occur during asteroid impacts and the rich variety of diaphites that can form. By controlling the layer-by-layer growth of structures, it should be possible to design materials that are both ultra-hard and also ductile, as well as have adjustable electronic properties from a conductor to an insulator. Their study opens the door to new carbon materials with exciting mechanical and electronic properties that may result in new applications ranging from abrasives and electronics to nanomedicine and laser technology.