Scientists solve mystery of rare blue diamonds

A team of scientists analyse 46 blue diamonds to trace how deep in the earth do they come from and how exactly do they get their precious colour. The study, published in Nature on August 1, found that type 11b diamonds were formed deep into the Earth, at least as deep as the transition zone between the planet’s upper and lower mantle. They got their precious blue colour because of boron, an element that is found on the Earth’s surface. Blue diamonds were formed deep between 410 and 660 kilometres below the surface. Some of the diamonds analysed for the study showed indications that they came from a location deeper than 660 kilometres.
The most common gems can be fetched from between 150 and 200 kilometres. If blue diamonds are found this deep into the Earth’s mantle, how did they come in contact with boron, which was abundant on the Earth’s surface? The team of scientists, headed by Evan Smith of the Gemological Institute of America, concluded that the boron seeped from the seafloor that was pushed down into the Earth’s mantle through a process called subduction, or when one tectonic plate slid beneath another. The boron merged into water-rich minerals that crystallised after undergoing geochemical reactions that take place between seawater and the rocks found in the oceanic plate.