A red diamond represents the absolute pinnacle of scarcity within the world of gemstones. This fancy colored diamond is composed of pure carbon, sharing the same fundamental structure as its colorless counterparts. The intense red hue elevates these stones, which are widely recognized as the rarest of all colored diamonds, a category that includes blues, pinks, and yellows. Their exceptional scarcity means that encountering a truly red stone is a significant event in the global gem market.
Quantifying the Extreme Rarity
The rarity of finding a red diamond primarily drives its astronomical value. In the entire history of gemology, fewer than 30 true “Fancy Red” diamonds are known to exist globally. This figure refers only to stones graded by laboratories like the Gemological Institute of America (GIA) as having an unmodified red color. The GIA did not issue a single grading report for a diamond with a pure red color descriptor during the 30-year period between 1957 and 1987.
Most of these scarce diamonds are extremely small, typically weighing less than one carat. A red diamond exceeding one carat is considered a monumental find, making any such stone an immediate historical artifact. This scarcity contrasts sharply with other colored diamonds, such as yellows, which are found in relative abundance. Even blue and pink diamonds, themselves rare, are found in greater numbers and larger sizes than their red counterparts.
The Unique Formation of Red Color
The origin of the red color is entirely different from the mechanism that colors most other fancy diamonds. Yellow and blue diamonds, for example, owe their color to chemical impurities like nitrogen and boron trapped within the crystal structure. Conversely, red diamonds are made of nearly pure carbon and do not contain these trace elements. Their color is instead a result of a physical deformation in the diamond’s atomic lattice.
This structural defect is known as plastic deformation. It occurs as the diamond crystal endures immense pressure and heat during its ascent from the deep earth. The pressure causes the carbon atoms to shift and glide along their planes, creating internal stress lines in the crystal. This distortion absorbs the green and blue wavelengths of visible light, allowing only the intense red light to be transmitted to the eye.
Geographical Sources and Key Examples
For decades, the Argyle Mine in the East Kimberley region of Western Australia was the world’s only consistent source for red diamonds. While the mine produced over 90% of the world’s supply of pink and red diamonds, the proportion of red stones was an incredibly tiny fraction of its total output. The mine ceased operations in November 2020, removing the world’s primary source of these ultra-rare stones.
The closure of Argyle potentially makes future discoveries of red diamonds even more infrequent. The most famous example, and the largest known internally flawless red diamond, is the 5.11-carat Moussaieff Red Diamond. Another notable stone is the 0.95-carat Hancock Red Diamond, which set a per-carat price record at auction in 1987. These examples demonstrate that even stones under one carat can command historical significance and immense value.