Diamonds are products of Earth’s recycled seabeds



A recent study focuses on the formation of diamonds. The research published in Science Advances concludes that diamonds contain traces of salt which hints on its formation from recycled seabeds found deep within Earth’s crust. Researchers confirmed that most of the diamonds are formed through this method while others are created by crystallization which melts deep in the mantle.

A team led by scientists from Goethe Universität and Johannes Gutenberg Universität in Germany recreated extreme pressures and temperatures two hundred kilometers underground. Through this experiment scientists inferred that the seawater in sediment reacts in the right way to produce the balance of salts found in diamonds.

“There was a theory that the salts trapped inside diamonds came from marine seawater, but couldn’t be tested. Our research showed that they came from marine sediment,” reported Dr Michael Förster, one of the lead authors on the paper.

Furthermore, the study also revealed that diamonds which are crystals of carbon are formed beneath the Earth’s crust in very old parts of the mantle. These are brought to the surface via volcanic eruptions of magma known as kimberlite. The study draws attention to two kinds of diamonds, gem diamonds and fibrous diamonds. Fibrous diamonds grow more quickly than gem diamonds but are cloudy and not so attractive to jewelers, on the other hand gem diamonds are made of pure carbon. It is the sediment of sodium, potassium and other minerals found on the diamonds that reveal information about the diamonds formation. “We knew that some sort of salty fluid must be around while the diamonds are growing, and now we have confirmed that marine sediment fits the bill,” says Dr Förster.

The research team conducted an experiment by adding pressures between four to six gigapascals and temperatures between 800°C and 1100°C, these measurements were corresponded to depths between 120 and 180 kilometers below the surface. The test proved formation of salts balanced with sodium and potassium which also matched with small traces of salt found in the diamonds.

“We demonstrated that the processes that lead to diamond growth are driven by the recycling of oceanic sediments in subduction zones. 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,” concludes Dr Förster.