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Rare diamonds that fell to Earth came from a dwarf planet, scientists say

A collection of 18 rare diamond-bearing meteorites from around the world come from an ancient dwarf planet that crashed into a giant asteroid 4.5 billion years ago, according to new research.

The specimens contain lonsdaleite – an unusual super hard hexagonal shape of the 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 make up less than 1% that fall to Earth.

A study of meteorites can bring benefits to industrial processes.

“So nature has provided us with a process to try and replicate in industry,” said lead author Professor Andy Tomkins, a geologist at Monash University in Melbourne, Australia.

“We believe lonsdaleite could be used to make tiny, ultra-hard machine parts if we can develop an industrial process that promotes the replacement of preformed graphite parts with lonsdaleite.”

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

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

In diamonds, however, the carbon atoms are bound together in an extremely rigid “tetrahedral” shape. Combined with the strong links, this makes them extremely tough.

Yet it breaks and crumbles at high enough pressures. Tiny flaws in a crystal can also weaken it, making the diamond vulnerable to decay.

This does not occur with lonsdaleite in the ureilite meteorites of the dwarf planet’s mantle. The hexagonal structure makes it potentially harder than regular diamonds, which are cubic.

“This study is categorical proof that lonsdaleitis exists in nature,” says lead author Professor Dougal McCulloch from RMIT University in Melbourne. “We also discovered the largest lonsdaleite crystals known to date, up to a micron in size – much, much finer than a human hair.”

The international team said their odd formation opens the door to dramatic improvements in manufacturing.

They used state-of-the-art electronic scanners to capture solid, undamaged slices, providing “snapshots” of the formation of lonsdaleite and regular diamonds.

“There is strong evidence that there is a recently discovered formation process for lonsdaleite and ordinary diamond,” McCulloch said.

Lonsdaleite is believed to have formed at high temperature and moderate pressures, almost perfectly preserving the shape and textures of pre-existing graphite.

“Later, the lonsdaleite was partially replaced by diamond as the environment cooled and the pressure decreased,” Tomkins said.

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

The study suggests that all ureilite meteorites are remnants of the same protoplanet. It also supports the theory that today’s planets were forged from the remains of these early worlds.

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

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