When many people picture a diamond, they imagine a brilliant, faceted gemstone sparkling under a spotlight. A diamond in its natural state is a solid form of the element carbon, crystallized deep within the mantle under immense heat and pressure. The journey from this raw, greasy-looking pebble to a dazzling jewel is a complex process of scientific analysis and precise craftsmanship.
The Uncut Appearance of Rough Diamonds
Newly discovered diamonds rarely possess the transparent, highly reflective look of a finished gem, appearing instead as dull, translucent stones. The most common shape is the octahedron, which resembles two four-sided pyramids joined base-to-base, though dodecahedrons and irregular shapes are also found. The surface often has a faint, greasy or waxy luster, sometimes covered by a thin, opaque film referred to as “nyf”.
Specific growth marks, such as trigons, help identify the material. These are tiny, triangular-shaped indentations etched into the surface, and their orientation indicates the material’s atomic structure. Rough diamonds also frequently contain internal flaws, known as inclusions, which can be small mineral deposits, growth lines, or tiny fractures.
The majority of rough diamonds are not colorless, but instead exhibit tints of yellow, brown, or gray due to trace elements like nitrogen. These colors make the unpolished stone appear cloudy or opaque. Only a small fraction of all mined diamonds are found to be perfectly clear and colorless in their rough state.
Geological Settings and Host Rocks
Diamonds form deep beneath the Earth’s surface, approximately 100 to 250 miles down, under temperatures exceeding 2,000°F. They are brought to the surface through rare, explosive volcanic eruptions that create vertical columns of rock called kimberlite or lamproite pipes. These carrot-shaped geological structures are the primary source of the world’s diamonds, with the stones embedded directly within the cooled igneous rock.
Weathering and erosion have worn down these primary host rocks, washing diamonds out of the pipes and carrying them downstream into rivers and coastal areas. These secondary locations, known as alluvial deposits, contain diamonds mixed with gravel and other materials. Miners often find these diamonds in riverbeds, where their density causes them to settle alongside other heavy minerals.
Distinguishing Rough Diamonds from Common Minerals
Identifying a rough diamond requires more than a simple visual inspection, as many common minerals like quartz, topaz, or glass can look similar. Confirmation involves testing the material’s extreme hardness, which is rated as 10 on the Mohs scale. This means a diamond can scratch nearly any other mineral, and a common test involves seeing if the suspect material can leave a mark on corundum, which is rated as 9.
The stone’s specific gravity, or density, is higher than most other minerals found alongside it. A diamond has a density of approximately 3.52 g/cm³, noticeably heavier than quartz (around 2.62 g/cm³). This density difference is used in mining processes, such as grease tables, where diamonds adhere to grease while other materials are washed away.
The crystal form also provides clues; the natural octahedral shape of a diamond contrasts with the six-sided hexagonal structure of quartz crystals. Diamonds have high thermal conductivity, a property measured by specialized probes to quickly differentiate them from most look-alikes. Industrial sorting processes also rely on the fact that diamonds glow when exposed to shortwave X-rays.
From Rough Crystal to Polished Gem
The transformation of a rough crystal into a polished gem is a multi-stage process that begins with detailed planning. Advanced scanning technology and computer software map the stone’s internal structure and calculate the best way to cut it to maximize final value and carat weight. This planning determines where the stone will be divided to avoid inclusions and yield the largest possible finished diamonds.
The rough stone is cleaved along its natural plane of weakness or sawn with a laser or a diamond-coated blade. Since only a diamond can cut another diamond, the tools used are coated or made with diamond dust. Following this initial split, the stone undergoes bruting, where it is shaped into a preliminary round form by grinding it against another diamond.
The final steps involve faceting and polishing, which unlock the stone’s brilliance and fire. Skilled technicians carefully create the small, flat surfaces, or facets, by holding the diamond against a rotating wheel coated with fine diamond powder. This process reveals the diamond’s high refractive index of 2.42, allowing light to reflect and refract in the dazzling way the public recognizes.