The red diamond is the rarest color-grade of diamond found anywhere on Earth. This carbon-based mineral is an extreme geological outlier because the precise conditions for its deep, saturated hue are almost never met in nature. Unlike other colored diamonds that owe their existence to trace chemical impurities, the striking red color results from a unique physical deformation occurring deep within the planet. This rare formation process and single dominant source cement the red diamond’s status as a highly sought-after specimen.
The Primary Global Source
The vast majority of the world’s gem-quality red diamonds trace their origin to a single location: the Argyle Mine in the remote Kimberley region of Western Australia. Although a handful of non-commercial red diamonds have been found in places like Brazil and Russia, their contribution to the global supply is minimal. Argyle was primarily famous for supplying over 90% of the world’s pink diamonds, but it also served as the consistent source for the few red stones discovered annually.
The Argyle Mine ceased all mining operations in November 2020 after nearly four decades of production due to the depletion of economically viable ore reserves. This closure instantly removed the sole reliable source of red and pink diamonds from the global market. The end of supply from Argyle has significantly intensified the scarcity of existing stones, making them an exclusive commodity for collectors and a finite geological legacy.
Geological Requirements for Formation
The Argyle pipe is a geological rarity because it is a lamproite deposit, rather than the far more common kimberlite rock that typically brings diamonds to the surface. Lamproite is an ultrapotassic igneous rock that erupted through the Halls Creek Orogen, a weaker zone that experienced intense tectonic collision and faulting.
The deposit’s location within this active, faulted collision zone is considered the direct cause of the Argyle diamonds’ unique physical characteristics. This tectonic environment subjected the diamonds to immense and prolonged shear stress after their initial formation in the mantle. This geological pressure created the specific crystal defects necessary to produce the full color spectrum, ranging from champagne to pink and red.
The Scientific Cause of the Red Hue
The intense red color of these diamonds is a purely structural phenomenon, setting them apart from diamonds colored by chemical elements. While yellow or blue diamonds receive their color from trace impurities like nitrogen or boron, red diamonds are essentially pure carbon. They gain their color from a physical defect known as plastic deformation.
This deformation occurs when the diamond crystal is subjected to extreme, non-uniform pressure deep within the Earth. The immense stress causes carbon atoms to shift slightly, creating parallel lines of irregularity called glide planes. These structural defects alter how the crystal absorbs light across the visible spectrum. The glide planes specifically absorb blue and green wavelengths, leaving only red light to be transmitted and reflected.
Defining Characteristics and Rarity
The extreme rarity of red diamonds is reflected in their size and specific grading criteria. Most natural red diamonds recovered are notably small, with the vast majority weighing less than one carat. Only a handful of known specimens exceed five carats; the largest faceted example, the Moussaieff Red, weighs just 5.11 carats.
When graded by gemological laboratories, red diamonds are unique because they are only assigned a single intensity grade: “Fancy Red.” Unlike other colored diamonds graded as Fancy Light, Intense, or Vivid, any diamond achieving true red saturation is automatically considered peak intensity. Pure “Fancy Red” stones without modifying colors are the most sought-after. However, many stones are graded with secondary hues such as “Purplish Red” or “Brownish Red,” which typically results in a lower value compared to a fully saturated, pure red stone.