Red diamonds are a tangible reality and represent the rarest type of natural colored diamond. These gems exhibit a crimson hue and are highly sought-after by collectors. Their scarcity and unique origin story set them apart from other gemstones. The science behind their color is distinct, involving a geological process that creates a structural anomaly rather than a chemical impurity.
The Definitive Answer: Existence and Rarity
Red diamonds exist, but their presence is so limited that they are considered the rarest type of diamond found anywhere in the world. The global population of true “Fancy Red” diamonds is estimated to be fewer than 30 known stones, including those in private collections and museums. Most of these diamonds weigh less than one carat.
The Argyle Mine in Western Australia was the primary source for the world’s most saturated pink and red diamonds for decades. The mine closed in 2020, producing only a small, unpredictable handful of these stones annually. The closure means the supply of newly-mined red diamonds has effectively ceased, increasing the rarity of existing stones. While smaller quantities have been found in Brazil and various African countries, Argyle specimens were prized for their pure red tone.
The Unique Mechanism of Red Coloration
The red color in these diamonds does not come from trace elements, which is the mechanism for most other colored diamonds. While nitrogen causes yellow hues and boron causes blue, red diamonds are composed of virtually pure carbon. Instead, the color originates from a rare geological phenomenon known as “plastic deformation.”
This process involves an alteration of the diamond’s internal crystal structure that occurs deep within the Earth under immense pressure. As the diamond is forced toward the surface through volcanic kimberlite pipes, the extreme pressure creates stress laminations, or “glide planes.” These planes cause the carbon atoms to become structurally displaced, and these defects change how the diamond absorbs and reflects light.
The structural distortion causes the diamond to absorb light across the visible spectrum, except for the deepest red wavelengths. This selective absorption allows only the red color to be transmitted to the observer. Red diamonds are essentially pink diamonds where the structural deformation is so intense that the resulting color saturation crosses the threshold into true red.
Comparing Red Diamonds to Other Fancy Colors
Red diamonds occupy the highest tier of the fancy color diamond hierarchy. The distinction is apparent in the grading system used by gemological laboratories. While most colored diamonds are assigned intensity grades like Fancy Light, Fancy Intense, or Fancy Vivid, red diamonds are almost exclusively graded as “Fancy Red” with no modifying intensity term.
This singular grading reflects that any diamond saturated enough to be classified as red already possesses the highest possible color intensity. Only a handful of other colors, such as black and white, are characterized by a single intensity grade. Red diamonds may be accompanied by secondary color modifiers like purplish-red or brownish-red, but a pure Fancy Red diamond without any secondary hue commands the highest market valuation.
Due to their scarcity, red diamonds consistently achieve significantly higher price-per-carat values compared to other fancy colors. These values often reach into the hundreds of thousands or millions of dollars per carat.
Notable Red Diamonds in History
The history of red diamonds is tied to the few notable specimens that have surfaced. The Moussaieff Red Diamond is the largest known Fancy Red diamond in the world, weighing 5.11 carats. This modified triangular brilliant-cut stone was discovered in Brazil in the 1990s and possesses Internally Flawless clarity, which is rare for a stone formed by structural deformation.
Another historically significant example is the Hancock Red, a 0.95-carat round brilliant. This stone set a world record for the highest price per carat of any gemstone when it sold at auction in 1987. The Hancock Red, which has a purplish-red modifier, sold for over $926,000 per carat. Along with the 5.03-carat De Young Red, these stones prove the red diamond’s immense commercial significance.