Diamonds are extremely valuable, but new research supports the theory that they're likely just recycled seabed, albeit, "cooked" for millions and millions of years.
The Origins Of Diamonds
These precious rocks take so long to form that it's challenging for scientists to trace their origins accurately. Traces of salt found in plenty of diamonds offer clue, however.
"There was a theory that the salts trapped inside diamonds came from marine seawater, but couldn't be tested," explained study lead author and professor Dr. Michael Förster of Macquarie University in a statement, adding that their research was able to show that these salts originated from marine sediment.
According to Live Science, one theory is that huge slabs of the sea floor containing plenty of minerals drop rapidly into the Earth's mantle where the crushing pressures and ultra-high temperatures cause them to crystallize. In time, these crystals combine with a specific type of volcanic magma known as kimberlite and burst onto the surface as diamonds.
Recreating Diamond Formation
In the new study published in the journal Science Advances, Förster and the rest of the team used fibrous diamonds, which are diamond variants that are not pure carbon.
Instead, this cloudy type of diamond contain small amounts of sodium, potassium, and other minerals. While they're less valuable to jewelers and collectors, fibrous diamonds are extremely useful to geologists as they reveal more about the history and environment of its formation.
Fibrous diamonds are known to grow more rapidly than gem diamonds, which means they end up trapping tiny pockets of liquid while forming.
To see whether these salty liquids are from the ocean, the authors conducted experiments that recreated the conditions of diamond formation.
Marine sediment samples were placed in a vessel with a peridotite rock, which is the most common type of rock in the section of the mantle where diamonds are created.
Then, these were exposed to the extreme pressures and temperatures found 75 to 112 miles (120 to 180 kilometers) under the Earth's surface. Pressures ranged from four to six gigapascals, while temperatures varied between 1472 and 2012 degrees Fahrenheit (800 to 1100 degrees Celsius).
Under these conditions, the team found that salts formed with a similar composition of salts found in diamonds.
"We demonstrated that the processes that lead to diamond growth are driven by the recycling of oceanic sediments in subduction zones," said Förster. "The products of our experiments also resulted in the formation of minerals that are necessary ingredients for the formation of kimberlite magmas, which transport diamonds to the Earth's surface."