Tiny invisible diamonds tell Australia’s tectonic story

A unique type of diamond has been discovered in Australia for the first time, but they are invisible to the naked eye.

Researchers from James Cook University in Queensland have found rare metamorphic diamonds in rocks along the Clarke River Fault, west of Paluma in the upstate, according to Science Advances Journal.

But before anyone grabs their mining tools to find their own shiny rock, these diamonds can only be seen with the help of a laser and a microscope, according to the university’s Ioan Sanislav.

“Don’t go to Paluma and start looking for them. Even for us it was very difficult to find them,” he said.

“We had to analyze many, many thin sections of rock, and to prove the diamonds were there took about a year and a half.”

Metamorphic diamonds form in subduction zones, where two land masses collide, causing the edge of one tectonic plate to plunge beneath another and sink deep inside the Earth.

Metamorphism takes place over millions of years and generates a massive increase in pressure and temperature as the rocks, once at the surface, descend into the Earth’s mantle before rising as metamorphic rocks containing the tiny diamonds.

These diamonds differ from the usual diamonds mined around the world and fashioned into jewelry.

Sanislav said the team used a Raman microscope to identify the diamonds, firing a laser beam at a rock sample to determine the presence of hidden minerals in the rock.

“The light is then scattered and each mineral has a characteristic response, which comes back to the detector,” he said.

Metamorphic diamonds are only known to exist in six other places around the world, ranging in size from microscopic to nanoscopic.

“In some places there are metamorphic diamonds that you can’t even see under a microscope. You just see a reading in the rock that indicates they’re in there,” he said.

Sanislav said he was brought in to investigate the area after a student found evidence to suggest rocks along the fault had undergone high-pressure metamorphism.

“This discovery will influence our understanding of the tectonic patterns and formation of Australia’s east coast,” he said.

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Australian Associated Press is an Australian news agency.

Sarah C. Figueiredo