A natural diamond is a rough, unpolished crystal extracted directly from the Earth. Its appearance is quite distinct from the brilliant, faceted gemstones seen in jewelry. Straight from the mine, the stone lacks the fiery sparkle that cutting and polishing create. This unrefined state reveals the geological history of the gem, showing a form that is often more opaque and less immediately impressive than its finished counterpart.
The Raw Appearance of Uncut Diamonds
The external surface of an uncut natural diamond typically possesses a greasy or waxy luster, not the high, glassy reflection of a cut stone. This dull sheen helps distinguish the rough crystal from other minerals like quartz. To the untrained observer, a rough diamond may look much like a common pebble or a piece of dull, translucent glass.
Many rough diamonds appear opaque or translucent, preventing a clear view of the interior. The outer texture often displays various markings, which are signs of its growth and journey to the surface. One of the most telling surface features is the presence of trigons, minute, triangular etchings or depressions on the crystal faces.
These trigons are formed during the diamond’s growth or through a process of natural dissolution, indicating the crystal’s atomic structure. Other common surface marks include growth lines, etch pits, and small fractures. The overall impression is that of a dense, irregularly shaped mineral, sometimes with a slightly rounded or blocky structure.
Color and Clarity Variations
Most diamonds fall within the normal color range, which is graded on a scale from D (colorless) to Z (light yellow or brown). The presence of nitrogen in the crystal structure is the common cause for the yellowish or brownish tint found in most natural diamonds.
Diamonds that exhibit a color beyond the Z grade, or any color other than shades of yellow or brown, are classified as “fancy color” diamonds. These include hues of pink, blue, red, and green. The intensity and purity of the color, rather than its absence, determine the value of a fancy color diamond.
Clarity refers to the presence of internal features known as inclusions, which are essentially the diamond’s birthmarks. These internal flaws can be trapped foreign crystals, small cracks called “feathers,” or clusters of microscopic pinpoints that create a hazy “cloud” in the stone. A rough diamond may show these inclusions visibly, affecting its transparency and overall appearance.
Common Crystal Forms
The external shape of a natural diamond relates to its internal atomic structure, which belongs to the cubic crystal system. The most common and ideal crystal habit for a rough diamond is the octahedron, which looks like two four-sided pyramids joined base-to-base. This eight-sided form reflects the uniform arrangement of carbon atoms within the stone.
However, perfect octahedrons are less common, as most natural diamonds have been partially dissolved or resorbed by the surrounding magma during their ascent to the Earth’s surface. This process results in crystals with rounded edges, striated faces, and less distinct forms. Other geometric shapes, such as cubes (six square faces) and dodecahedrons (twelve diamond-shaped faces), are also found, though less frequently than the octahedral form.
The rough stone’s initial form dictates how a cutter will approach the planning process to maximize the weight and quality of the final polished gem. The presence of twinning, where two crystals grow together in opposite directions, can also result in flattened, triangular shapes known as macles.