A raw diamond is a naturally occurring mineral composed of carbon atoms arranged in a rigid crystal structure. This “rough” or “uncut” stone is the state in which the diamond is recovered from the Earth, looking far different from the sparkling gems typically set in jewelry. The transformation from this dull, unassuming crystal to a brilliant, polished gemstone involves a meticulous process of human modification. Understanding the raw form is the first step to appreciating the remarkable transformation that creates the world’s most desired jewels.
Defining the Uncut Stone
The formation of a diamond begins with pure carbon deep within the Earth’s mantle, typically at depths of 90 to 155 miles (150 to 250 kilometers) below the surface. Here, carbon is subjected to extreme geological forces, including temperatures exceeding 2,000°F and immense pressures of over 45 kilobars. These intense conditions force the carbon atoms to crystallize into the dense, tetrahedral lattice structure that defines a diamond, rather than the much softer structure of graphite.
After their initial formation, these ancient carbon crystals are carried toward the surface through rare, high-speed volcanic eruptions. They are primarily found embedded within igneous rock formations known as kimberlite pipes, which are the remnants of these deep-source eruptions. Erosion can also liberate diamonds from their source rock, leading to secondary deposits in riverbeds, known as alluvial deposits. The chemical composition of a raw diamond is almost entirely carbon, usually about 99.95%.
Physical Traits of Raw Diamonds
In its natural state, a raw diamond rarely resembles the cut and polished gems seen in stores; it often appears rough, unpolished, and sometimes opaque. The surface may have an oily or waxy sheen, which is a characteristic used in some mining processes to separate diamonds from other minerals. Raw diamonds can also contain natural imperfections or inclusions, which may appear as cloudy areas or specks trapped inside the stone during its formation.
The shape of the raw stone is dictated by its crystal habit, the preferred growth pattern of the carbon atoms. The most common shape for gem-quality rough diamonds is the octahedron, which looks like two pyramids joined at the base. Other common crystal forms include the dodecahedron, which has twelve faces, and less symmetrical or irregular shapes. Raw diamonds also exhibit a range of colors, from colorless to shades of yellow, brown, and even rare hues like pink or blue.
Transitioning from Raw to Gem
Once recovered, the raw diamonds undergo an initial sorting to distinguish between gem-quality and industrial-quality stones. Only a fraction of mined diamonds are deemed suitable for jewelry, with the majority being used for industrial applications due to their exceptional hardness. For those destined to become gems, the process begins with detailed planning.
Specialized equipment is used to analyze the raw crystal’s structure, inclusions, and flaws to determine the optimal way to cut it. The cutter’s goal is to maximize the yield and value from the rough stone, which often involves deciding how to split the crystal to produce the largest possible polished diamond. The initial transformation involves cleaving or sawing the rough diamond, sometimes using lasers or a diamond-coated saw blade, to separate it into workable pieces.
This initial cut is carefully executed along the diamond’s natural cleavage planes to prevent fracturing the stone. The resulting pieces are then mechanically bruted to establish the rough outline of the final gem, creating a rounded girdle. After this shaping, the stone moves to the polishing stage, where facets are systematically added to create the brilliance and fire that the world associates with a finished diamond.