Scientists are piecing together the mystery behind blue diamonds

A new study is bringing us closer to solving the mystery of how blue diamonds are made.

Accounting for about 0.02 percent of all diamonds, blue diamonds are the rarest diamonds on Earth, The Washington Post explained. While colorless diamonds are made up of a crystalline structure of carbon atoms at the molecular level, blue diamonds are formed when that structure is interrupted by boron atoms — a rare impurity that has fascinated people for hundreds of years, since the discovery of the Hope Diamond, the world's most famous blue diamond.

Scientists have long guessed at what might cause the atomic structure of blue diamonds to change — and for the first time, they have a theory, a study published in the journal Nature on Wednesday reveals. Researchers analyzed the impurities trimmed away from cut blue diamonds and discovered traces of minerals that point to these diamonds forming from two types of rock: the oceanic crust from the Earth's surface and the ocean mantle that lies beneath it. The shifting of tectonic plates can push these two types of rocks together, creating "a match made in the abyss" that could lead diamonds to absorb the boron naturally found in seawater and thus turn blue, The Washington Post explained.

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The findings suggest that blue diamonds form up to four times deeper underground than colorless diamonds — around 400 miles beneath the Earth's surface. While the theory isn't proven yet, it is "a very compelling argument," said Jeffrey E. Post, a curator at the Smithsonian's National Museum of Natural History. Read more about the study at The Washington Post.