There are many sayings, legends, theories, and misconceptions surrounding diamonds, fitting for one of the most valuable gems on our planet! A few things we know for certain about diamonds is that they are beautiful, they are rare, and they are very, very old. The combination of extreme age and rarity has made it difficult for scientists, even after all this time, to discover exactly how natural diamonds are formed.

The theory behind salty diamonds

Scientists know that it takes extreme levels of pressure and heat, over very long periods of time, to create diamonds. These conditions can only be found beneath the planet’s surface or in specialized lab equipment. However, there is still a lot of information missing from our understanding of what else goes into the forming of one of these precious gemstones.

One prominent theory on diamond creation is that they form, not only under the ground but under water. This theory posits that diamonds are created when parts of the seabed (known as oceanic plates) grind beneath the continental plates. The sites where this happens are called tectonic subduction zones. At these zones, seawater and all the minerals (including salt) it contains, along with everything else on the ocean floor is drawn down hundreds of miles deep beneath the earth. Once down below the Earth’s mantle, the minerals are subjected to pressure tens of thousands times greater than we experience on the surface of the planet, along with extreme heat, in other words, the perfect environment for diamonds to form.

New evidence for ocean-based diamonds

Some scientists who study the creation of diamonds have long held to this particular theory of their oceanic origination for a few solid reasons. The first is that blue-tinted diamonds (most famous among these is the Hope diamond) most likely get their unique color from certain oceanic minerals. Another good reason is the existence of a class of gemstone known as fibrous diamonds. Fibrous diamonds aren’t pretty enough to be worn in any jewelry because they have visible, cloudy deposits of sodium, potassium, and other minerals inside of them. All of these minerals can be found commonly in seawater and marine sediment (dirt from the ocean floor)!

While fibrous diamonds may not be as beautiful as clearer gemstones, they contain a wealth of information for scientists to study. Michael Forster, a professor at Macquarie University in Australia recently lead a study that lends new weight to the theory. Since accurately tracing the origins of an actual diamond is practically impossible given the time spans and extreme environments involved, Forster and his team decided to test if the mineral deposits in fibrous diamonds could have come from seawater by working backward.

Using specialized pieces of lab equipment, Forster and his colleagues took samples of marine sediment, mixed in some of the mineral peridotite (commonly found at the depths scientists believe diamonds are formed), and subjected these samples to extreme pressure and temperature that matches those found beneath the Earth’s crust. What the scientists discovered is that when the samples were subjected to pressures of 4 to 6 gigapascals (that’s 40,000 to 60,000 times the pressure on the surface) and temperatures of 1,500 to 2,000 degrees Fahrenheit, salt crystals formed with nearly identical properties to natural fibrous diamonds!

While this doesn’t prove beyond doubt that diamonds have their origins deep below the ocean floor, it does strongly suggest that they do. Forster pointed out that they have simply proven that marine sediment matches the salty mineral deposits scientists knew had to be present during the formation of these diamonds. Could there be other explanations? Yes, but diamonds could very well be pieces of ocean history that we can wear.