Diamonds are a geologists best friend. For proof of that, look no further than a recently mined diamond that contained a mineral that had never been seen in nature, until now.
The discovered mineral, called calcium silicate perovskite (CaSiO3) was discovered, trapped inside a diamond excavated from South Africa's Cullinan mine (which is the most famous mine for yielding the world's largest diamond in 1905, as part of which now adorns the crown jewels of the United Kingdom).
The finding provides an important clue to the puzzle of how Earth's inner structure behaves. While the mineral is rare to the human eye, calcium silicate perovskite may be shockingly ordinary deep inside the Earth, in fact, it is thought to be the fourth most abundant mineral inside the planet, especially prevalent in slabs of oceanic crust that have plunged into the planet's mantle at tectonic boundaries.
"Nobody has ever managed to keep this mineral stable at the Earth's surface," study co-author Graham Pearson, a professor in the University of Alberta's Department of Earth and Atmospheric Sciences, said in a statement. "The only possible way of preserving this mineral at the Earth's surface is when it's trapped in an unyielding container like a diamond."
In a new study, Pearson and his colleagues analysed the tiny diamond (roughly 3 millimetres across) excavated from Cullinan less than 1km below the Earth's surface. Despite this relatively shallow depth, the researchers determined that the crystal was an example of a "deep diamond" that most likely had been formed about 700km below the Earth's surface, derived from a subducted slab of ocean crust and exposed to some 240,000 atmospheres of pressure.
"Diamonds are really unique ways of seeing what's in the Earth," Pearson said. "And the specific composition of the perovskite inclusion in this particular diamond very clearly indicates the recycling of oceanic crust into Earth's lower mantle. It provides fundamental proof of what happens to the fate of oceanic plates as they descend into the depths of the Earth."