Blue diamonds have been a mystery for centuries, but scientists are now learning new information about the secrets behind these precious, colorful stones. “The origin of blue diamonds is such an alluring question — you don’t see them very often,” says Kim Tait, a gem expert at the Royal Ontario Museum in Toronto. “And the famous ones, like the Hope diamond, have such mystique.”
The blue tint comes from traces of boron within the diamond. Only one of about 200,000 diamonds are blue, yet all diamonds form when carbon faces intense pressure and extreme heat deep inside of the earth.
Researchers studied 46 blue diamonds and used lasers to find any imperfections that might provide clues as to where and how they originated. Steven Shirey, a geochemist at Carnegie Institution for Science in Washington, said a “diamond is an extraordinary container, a time capsule.”
After studying their mineral content, scientists determined blue diamonds form much deeper in the ground than previously believed. While most common diamonds form about 100 miles below the earth’s surface, blue diamonds form roughly four times deeper. The findings were reported in the journal Nature.
Gemological Institute of America research scientist Evan Smith told Popular Science, “We now have a snapshot of the birthplace of this diamond. We were finding minerals trapped inside that you only get in the extreme depths of Earth. They’re the deepest diamonds anyone has ever analyzed.”
The boron in blue diamonds comes from the ocean floor being pushed down when the plates of the Earth’s crust collided, allowing the stones to absorb red light, which led to a blue hue. “Most of the impurities contained in these blue diamonds came from a very deep source,” says Dongzhou Zhang a scientist at the University of Hawaii. “This study tells us for the first time that blue diamonds are formed very deep in the interior of Earth.”