The black diamond is an enigmatic gemstone, captivating collectors and scientists alike with its intensely dark, opaque appearance. Unlike colorless, transparent diamonds, this unique material has a specific scientific classification that distinguishes it from other stones. To understand this gemstone fully, one must explore its proper name, its unusual structure, and how it differs from the more common treated stones found in the commercial market.
The Formal Name and Definition
The formal name for a natural black diamond is Carbonado, a term derived from the Portuguese word meaning “burned” or “charred.” While “black diamond” is the commonly accepted industry term, Carbonado is the scientific and historical classification for this distinct material. Brazilian prospectors gave it this name in the mid-19th century, noting its resemblance to charcoal.
Carbonado is defined by geologists as a rare, polycrystalline diamond aggregate. Unlike a traditional diamond, which is a single, large crystal of pure carbon, Carbonado is an impure, high-density cluster made up of minute, tightly-intergrown diamond crystals. The only known natural sources for this specific type of diamond are alluvial deposits found primarily in Brazil and the Central African Republic.
Unique Structure and Composition
The unique characteristics of Carbonado stem directly from its internal structure. Traditional diamonds possess a uniform, single-crystal atomic lattice, allowing light to pass through them. In contrast, Carbonado is polycrystalline, composed of countless microscopic diamond grains sintered together in random orientations.
This aggregate structure gives Carbonado its signature black color and opaque appearance. The stone contains a high concentration of dark inclusions, primarily graphite and amorphous carbon, trapped within the tiny diamond crystals. These dense, uniformly distributed dark materials absorb light rather than reflecting it, resulting in the deep, non-sparkling black hue. Furthermore, the polycrystalline nature of Carbonado makes it the toughest form of natural diamond, a property that made it valuable for industrial applications like drilling and grinding.
Differentiation from Treated Diamonds
The majority of “black diamonds” available in the commercial jewelry market are not natural Carbonado but are white or gray diamonds that have undergone specialized enhancement treatments. These treatments improve the diamond’s color and utilize stones that would otherwise be considered lower-quality due to numerous inclusions. The two most common methods for achieving the black color are high-pressure, high-temperature (HPHT) treatment or irradiation.
During HPHT treatment, a diamond is subjected to intense heat and pressure to permanently darken its internal fractures and inclusions, resulting in a saturated black color. Irradiation uses nuclear radiation to alter the diamond’s crystal structure, turning it a dark green that appears black to the naked eye. These treated stones are far more abundant and significantly less expensive than natural Carbonado. Only the rare, naturally occurring Carbonado possesses the unique polycrystalline structure and geological history that earns it the formal designation.