There are still many mysteries for science to solve. But that of the formation of a very particular type of diamond is no longer one of them. Researchers show how it can form from the encounter of an asteroid with a dwarf planet.
Lonsdaleite is a rather special form of diamond. Its carbon atoms, in fact, are arranged in a hexagon. While those of the classic diamond are cubed. It was discovered in 1967, in Meteor Crater (United States), the crater formed by the fall of a meteorite named Canyon Diablo, nearly 50,000 years ago. Today, researchers from the Royal Melbourne Institute of Technology (RMIT, Australia) have finally succeeded in proving that lonsdaleite does exist in its natural state.
To do this, the researchers used advanced electron microscopy techniques through which they were able to study solid, intact slices of a rare type of stony meteorite, ureilites. What to collect “strong evidence that there is a natural formation process for lonsdaleite that resembles what physicists do when making diamonds in the lab”. A kind of chemical vapor deposition at the very heart of space rocks.
Making materials harder than diamond
But to form lonsdaleite, it is necessary to start from a supercritical fluid, at high temperature and at moderate pressures. To preserve the shape and texture of the initial graphite. It is only when the environment cools and the pressure drops that the lonsdaleite is partially replaced by conventional diamond. A process that could have played out in our solar system about 4.5 billion years ago, shortly after a collision of a large asteroid with a dwarf planet.
Lonsdaleite’s hexagonal structure could make the material up to 60% harder than conventional diamond. The researchers therefore hope to have found, in nature, a process that they could exploit industrially to manufacture, from preformed graphite parts, tiny ultra-hard parts. Lowercase? Yes, because the largest lonsdaleite crystal found to date by researchers does not exceed one micron. That’s much less than… the thickness of a human hair!