The rarest type of diamond in the world

Unlike those that get their color from impurities, red diamonds are pure carbon and extremely rare, it is estimated that there are only 20-30 specimens in the world.

Red diamonds are sought after for their beauty, mystery and rarity. Photo: Levon Avagyan

Diamonds come in many shapes, sizes and colors, from stunning pink ones to ancient black ones believed to have formed in outer space. Among them, red diamonds are often the most highly valued and considered the rarest, with estimates that only 20 - 30 specimens exist in the world, IFL Science reported on June 13.

The majority of red diamonds are present in South Africa, Australia and Brazil. They get this rare color thanks to an unusual point in the formation process. Unlike diamonds that get their color from chemical impurities, such as nitrogen in the diamond structure, red diamonds are actually pure carbon. Rubies are famous red gemstones, but they get their color from corundum and chromium, not carbon.

The exact formation process of red diamonds remains a controversial mystery in geological circles. Some experts believe that the red color comes from plastic deformation, when pressure under the Earth's surface changes the diamond's molecular structure, according to Diamond Rocks London. Another explanation, says The Diamond Pro, is that deformations in the soil contribute to the red color.

The result of this process is that most red diamonds are quite small in size, only about half a carat to one carat. Still, they are among the most expensive diamonds in the world, with prices typically around one million dollars per carat. This type of diamond is so rare that, from 1957 to 1987, no pure red diamonds were graded by the Gemological Institute of America (GIA).

The world's largest red diamond, the Red Shield or Moussaieff Red, was discovered in Brazil in 1989 and sold for $8 million in 2021. The Red Shield weighs 5.11 carats, equivalent to about $1.6 million for per carat.