The Origin of Pink Diamonds

Pink diamonds are extremely rare. Most—about 90 percent—have come from one location: the Argyle mine in Australia. Now scientists think they know how the rosy gems ended up there.

Diamonds form when the element carbon (C) is exposed to intense pressure in Earth’s interior. Normally, the stones are clear. But if the crystals—solids whose atoms are arranged in a repeating pattern—are bent, they become pink. The sideways force required to bend diamonds’ crystal structure only occurs when there is a collision between tectonic plates—the slow-moving slabs of rock that make up Earth’s crust, or outer layer.

Argyle mine’s diamonds likely formed and turned pink when two landmasses collided 1.8 billion years ago to create a giant supercontinent known as Nuna. About 500 million years later, Nuna broke apart, causing volcanic activity. These eruptions likely pushed the pink diamonds toward the surface, says Hugo Olierook, a geologist at Curtin University in Australia.