A team of scientists analyzes 46 blue diamonds to track down the depth of the Earth from which they come and how exactly they get their precious color. 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 upper and lower mantle of the planet. They have their precious blue color because of the boron, an element found on the surface of the Earth. The blue diamonds were deeply formed between 410 and 660 km below the surface. Some of the Diamonds analyzed for the study showed signs that came from a place deeper than 660 kilometers.
The most common gems can be brought from between 150 and 200 km. If the blue diamonds are so deep in the mantle of the Earth, how did they come in contact with the boron, which was abundant on the surface of the Earth? The team of scientists, led by Evan Smith of the gemological Institute of America, concluded that boron filtered from the seabed that was pushed down into the mantle of the earth through a process called subduction, or when a tectonic plate slipped Under another. Boron was melted into water-rich minerals that crystallized after being subjected to geochemical reactions that are carried out between sea water and the rocks found on the oceanic plate.