Yes, diamonds can be black. Natural black diamonds are a highly sought-after and scientifically distinct variety of the gemstone. Their unique appearance results from a fundamentally different internal structure and chemical composition compared to traditional colorless diamonds. These opaque stones, often referred to geologically as carbonado, represent a fascinating anomaly in the world of mineral science.
Composition and Color Source
The intense black appearance of these diamonds results from a high concentration of microscopic inclusions scattered throughout the crystal structure. Unlike traditional diamonds, where value depends on the absence of inclusions, black diamonds owe their color entirely to these internal features. Specific minerals like graphite, hematite, and magnetite are commonly found as minute inclusions within the stone.
These minerals absorb virtually all light that enters the diamond, causing the stones to appear opaque instead of translucent. The density of these light-absorbing inclusions generates the deep, uniform black hue. Black diamonds also possess a polycrystalline structure, meaning they are composed of countless tiny diamond crystals fused together. This structure is different from the single-crystal structure of a colorless diamond. This opaque, polycrystalline nature prevents them from sparkling like typical diamonds, instead displaying a distinct metallic luster.
Unique Formation Hypotheses
The formation process of natural black diamonds (carbonados) is unique and distinct from the mantle-formed origin of traditional diamonds. Conventional diamonds crystallize deep within the Earth’s mantle under immense pressure and heat. Carbonados, however, are typically found in alluvial deposits and lack the characteristic geological settings of other diamonds, prompting theories of an extraterrestrial origin.
The leading scientific hypothesis suggests these diamonds formed in outer space. They may have originated in stellar supernovae explosions, where shock waves crushed carbon into dense aggregates, and were then delivered to Earth billions of years ago via asteroid impacts. This theory is supported by the diamond’s porous structure and the presence of trace elements, such as hydrogen and nitrogen. These elements indicate an origin in a hydrogen-rich interstellar environment. Carbonados have been dated to nearly four billion years old, a time when the Earth experienced heavy bombardment from large meteors.
Valuation and Grading Differences
Black diamonds do not conform to the standard 4 Cs (Cut, Clarity, Color, Carat) grading system used for colorless diamonds. The Gemological Institute of America (GIA) does not issue traditional grading reports for them. Their opaque nature and heavy inclusion count make a standard clarity assessment impossible. Instead, the color is typically graded using the single term “Fancy Black” to denote a uniform, high-intensity color.
The market value of a black diamond is heavily influenced by its color uniformity and whether the color is natural or enhanced. The rarity of a genuinely natural-color black diamond makes it significantly more valuable. However, many black diamonds sold are lower-quality, heavily fractured gray or off-color diamonds that have been treated. These treatments, involving heating or irradiation, create the uniform black hue by graphitizing the internal fractures. This enhanced color is stable, but the value of a treated stone is considerably lower than a rare, naturally colored carbonado.