Diamond-bearing meteorites came from dwarf planet 4.5 billion years ago

By Mark Waghorn via SWNS

Rare diamond-bearing meteorites came from an ancient dwarf planet that smashed into a giant asteroid 4.5 billion years ago, according to new research.

They contain lonsdaleite - an unusual hexagonal super-hard form of the precious gemstone. The discovery could hold the key to creating indestructible drills for mining.

The fragments fall into a category of space rocks called ureilites - which account for fewer than one percent that fall to Earth.

An analysis of 18 specimens collected from around the world has tracked them to a mysterious proto-world in the solar system.

Lead author Professor Andy Tomkins, a geologist at Monash University, Melbourne, said: "Nature has thus provided us with a process to try and replicate in industry.

"We think lonsdaleite could be used to make tiny, ultra-hard machine parts if we can develop an industrial process that promotes the replacement of pre-shaped graphite parts by lonsdaleite."

Diamonds are formed from the same carbon atoms that make up soft graphite in the center of pencils. The only difference is the arrangement.

Graphite is formed from flat sheets held together by weak attractive forces between each layer.

In diamonds, however, the carbon atoms are bound in an extremely rigid 'tetrahedral' shape. Combined with the strong bonds it makes them extremely hard.

The word 'diamond' itself is derived from the ancient Greek word adamas - or unbreakable.

Yet it does break and crumble at high enough pressures. Tiny flaws in a crystal can also weaken it - making the diamond vulnerable to disintegration.

This does not happen with lonsdaleite in ureilite meteorites from the mantle of the dwarf planet.

The hexagonal structure makes it potentially harder than regular diamonds - which are cubic.

Senior author Prof Dougal McCulloch, of Melbourne's RMIT University, said: "This study proves categorically that lonsdaleite exists in nature.

"We have also discovered the largest lonsdaleite crystals known to date that are up to a micron in size - much, much thinner than a human hair."

The international team says their strange formation opens the door to dramatic improvements in manufacturing.

They used state-of-the-art electron scanners to capture solid and intact slices - providing 'snapshots' of how lonsdaleite and regular diamonds formed.

Prof McCulloch said: "There's strong evidence there's a newly discovered formation process for the lonsdaleite and regular diamond.

"It's like a super-critical chemical vapor deposition process that has taken place in these space rocks - probably in the dwarf planet shortly after a catastrophic collision.

"Chemical vapor deposition is one of the ways people make diamonds in the lab - essentially by growing them in a specialized chamber."

It's believed lonsdaleite formed at high temperature and moderate pressures - almost perfectly preserving the shape and textures of the pre-existing graphite.

Prof Tomkins explained: "Later, lonsdaleite was partially replaced by diamond as the environment cooled and the pressure decreased."

It sheds light on a long-standing mystery regarding the emergence of carbon phases in ureilites.

The study in Proceedings of the National Academy of Sciences suggests all ureilite meteorites are remnants of the same proto-planet.

It also boosts the theory today's Solar System planets were forged from the leftovers of these early worlds.

Lonsdaleite is named after pioneering British crystallographer Dame Kathleen Lonsdale - the first woman Fellow of the Royal Society, a collective of notable scientists.