Qld scientists unearth new theory on origin of diamonds

When QUT professor Balz Kamber took a sledgehammer to a chunk of rock at a South African diamond mine, he found something that would end up being more valuable than the precious stones themselves – the key to how they form.

Kamber was rummaging through an old pile of waste rocks looking for one that contained a distinctive purple crystal called garnet harzburgite.

The rocks were mined anywhere between 1871 and 1914 but were themselves far older, with the one Kamber broke off believed to be 3.3 million years old.

Using this rock and others like it as a guide, Kamber and his colleagues have done fresh computer modelling that shows diamonds are rarer than previously thought.

Existing models of diamond creation suggest they are formed inside host rocks that also form these purple garnets, and that there used to be a lot of them but many were destroyed by huge tectonic forces over time.

However, Kamber said their new modelling suggested the diamonds were not destroyed, but that far fewer formed than previously thought.

“It was thought that diamonds were forming at the base of the continental plates millions of years ago, but that the moving and grinding of these plates would have destroyed many of the diamonds,” he said.

“By contrast, we suggest that diamond has always been rare – it only rarely formed, and actually survived to this day.”

QUT PhD candidate Carl Walsh, the lead research author, said they used the composition of the rock that Kamber had sourced and used it to create a new computer model for how diamonds were formed.