Study unlocks hidden secrets of how ultra-hard diamonds formed in rare meteorites

It has been speculated that lonsdaleite, a rare hexagonal form of diamond, is even harder and stronger than diamond itself.

Now an international team of scientists has discovered how the substance forms in ureilite meteorites, and suggested how that process could be replicated on Earth.

By using cutting-edge electron microscopy and synchrotron techniques they were able to create maps of the lonsdaleite, diamond, and graphite found in ureilite – a rare type of stony meteorite.

This showed the lonsdaleite formed from a supercritical fluid at high temperature and moderate pressures, which almost perfectly preserved the textures of the pre-existing graphite, but it was then partially replaced by diamond as the environment cooled and the pressure decreased.

Writing in Proceedings of the National Academy of Sciences (PNAS), researchers say the current method for producing industrial diamonds involves chemical vapour deposition, in which diamonds are formed onto a substrate from a gas mix at low pressures.

However, they say nature has now provided a process of creating lonsdaleite and, if it can successfully replicated in industry, the substance could be used to make tiny, ultra-hard machine parts and replace the pre-shaped graphite parts used across the world today.

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