A diamond mined less than a kilometer deep in the Cullinan mine (South Africa) – where the one in the photo comes from – has turned out to be the hiding place of a scientific treasure: calcium silicate perovskite, a mineral “that nobody has managed to keep stable on the earth’s surface ”, according to Graham Pearson, professor and geochemist at the University of Alberta (Canada) and author of the finding along with a group of colleagues from his center.
Calcium silicate perovskite is the fourth most present mineral on Earth, but it is only found in the planet’s mantle, which is approximately 30 to 2,900 kilometers deep. According to Pearson, the diamond that housed the sample would have withstood a pressure of 24,000 million pascals, equivalent to 240,000 atmospheres, and would have formed at a depth of about 700 kilometers, a relevant fact, since most of these precious stones are produced at between 150 and 200 kilometers deep.
The Canadian scientist clarifies that “the only way to preserve this mineral in the earth’s crust is for it to be trapped in a rigid container like a diamond.” In the laboratory, they have managed to create perovskites, materials with a crystalline structure similar to that of perovskite or calcium titanate, used in the manufacture of solar panels, among other things, but until now nobody had seen calcium silicate perovskite.
A look inside the Earth
What is relevant about the discovery, published in Nature, is that it offers magnificent indications of the composition of our planet. As Pearson explains, “Diamonds are unique to what is on Earth. The specific composition of the perovskite found in this diamond clearly indicates how the oceanic crust is recycled in the mantle. It is a test of what happens to oceanic plates when they descend into the depths. “
This is not the first time this geochemist has found something unique trapped in a diamond. In 2014, he was one of those responsible for the discovery of a sample of ringwoodite – the fifth most abundant mineral on Earth – trapped in a diamond from Juína, Brazil. It was the first time that this material appeared on the surface, apart from that obtained in the laboratory or that present in meteorites. As in the case of perovskite, it only forms at great depths and as a result of enormous pressures.
The ringwoodite fragment turned out to be very rich in water, which suggests that the transition zone of the terrestrial mantle – about which we still know little in terms of its composition -, located between 410 and 660 kilometers deep, could contain a quantity of water equivalent to that of all the oceans on the surface.
Photo: Petra Diamonds.
