The blue diamond has long intrigued people, even before the Smithsonian acquired the magnificent Hope Diamond, which weighs in at 45.52 carats, and now a new study has determined just why blue diamonds are actually blue and where they may have originated from.
Blue diamonds are exceedingly rare and difficult to find, and it has been estimated that out of 13.8 million diamonds, just 0.02 percent of these will end up being blue, according to ScienceAlert. And unlike their counterparts, they are also lodged much deeper inside the Earth, at a distance of approximately 400 miles beneath the ground. To put this immense distance into perspective, the International Space Station is currently lodged 254 miles above us in low Earth orbit.
Geologist Jeffrey E. Post, who is a curator at the Smithsonian, acknowledged that “we always knew there was something special about these diamonds.”
Blue diamonds have both delighted and confused scientists for a very long time as up until now research had not yet determined just how they formed, with lead author of the new study Evan M. Smith remarking that scientists were virtually clueless about blue diamonds up until very recently.
“We knew essentially absolutely nothing about where they grow.”
While diamonds are carbon atoms that have been crystallized, it was determined that blue diamonds contain boron, and it is an impurity like this that causes diamonds to become blue. However, this confused researchers, as boron should not be residing 400 miles beneath the Earth as it normally remains near its surface.
To try and gauge where the boron had come from, Smith and other scientists studied 46 blue diamonds. Similar to how plants grow in soil, diamonds come from rocks, and as they form some of the different materials around them can become stuck, according to Smith.
“When a diamond grows, sometimes it can envelop some of the surrounding material and trap it. The carbon crystals trap other minerals that are known as inclusions. I was able to study those inclusions to identify the minerals and start to build up a picture of the birthplace of blue diamonds.”
By studying these inclusions, Smith determined that there were minerals inside the blue diamonds like calcium silicates. These minerals only come into being if they are in a location where there is very high pressure, and Smith found that as the diamonds slowly pushed their way up through the Earth, these same minerals would have eventually shattered. Because of this, extremely tiny fragments ended up being lodged inside the diamonds.
After scrutinizing these ruptures, along with the different minerals that were retrieved from inside them, it was found that blue diamonds needed two quite different rock structures to form, namely ocean mantle and oceanic crust. This also helped to explain where the boron had come from as it is often present in seawater. And while the theory of where the boron definitively came from in blue diamonds is still just a theory, it is by far the best one that scientists have so far, at least without destroying some of these special gems.
The new study on the birthplace of blue diamonds and why they are blue has been published in the journal Nature.