A rough diamond is a naturally occurring diamond in its raw, unaltered state, found within the Earth. Unlike the polished gemstones commonly seen in jewelry, rough diamonds have an organic, unrefined appearance. They bear the marks of their geological formation, looking very different from the brilliant gems people typically imagine.
Key Visual Characteristics of Rough Diamonds
Rough diamonds exhibit various shapes depending on their crystal structure. Common forms include octahedrons, which resemble two pyramids joined at their bases. Others can be dodecahedral, cubic, or irregular. Macled diamonds, twinned crystals, often appear as flattened triangles.
Rough diamonds frequently display a range of colors, often yellow, brown, or gray. Rarer hues include pink, blue, or green. These colors result from trace elements, such as nitrogen (yellow) or boron (blue), or from structural defects within the diamond’s crystal lattice.
The surface of a rough diamond often reveals distinct textures. Common features include growth marks, triangular indentations called trigons, and etch pits. These characteristics can make the stone appear dull, frosted, or greasy. Such markings are natural evidence of the diamond’s growth processes.
Rough diamonds often contain internal flaws, known as inclusions, which impact their transparency and clarity. These can be tiny crystals, bubbles, or fractures. Common types include pinpoints, clouds (hazy clusters), and feathers (small cracks). The presence of these inclusions means rough diamonds typically lack the brilliant transparency of polished gems.
Distinguishing Rough Diamonds from Other Minerals
Rough diamonds possess a characteristic luster that helps differentiate them from other minerals. Even unpolished, they can exhibit an “adamantine” or diamond-like luster, appearing bright and reflective. However, their surfaces may also appear dull, glassy, or waxy.
Diamonds are extremely hard, ranking 10 on the Mohs scale. A rough diamond can scratch nearly all other minerals. Only a diamond can scratch another diamond.
Several minerals are often mistaken for rough diamonds. Quartz, for instance, forms hexagonal crystals and is significantly softer. Cubic zirconia and glass lack the distinct crystal structures and hardness of natural diamonds. Corundum (sapphires and rubies) has a different hexagonal crystal structure and is softer than diamond.
Diamonds are denser than many common look-alikes, with a specific gravity ranging from 3.1 to 3.5. This makes them feel heavier for their size compared to minerals like quartz, which has a specific gravity of 2.6 to 2.7.
Factors Influencing Rough Diamond Appearance
The appearance of rough diamonds is influenced by their formation conditions. Diamonds crystallize deep within the Earth’s mantle under extreme pressures and temperatures. Variations in these geological conditions, including pressure, temperature, and specific elements, dictate the diamond’s final crystal structure, color, and clarity.
Trace elements and impurities during formation directly impact a diamond’s color. Nitrogen, for example, is a common impurity that can cause yellow or orange hues, while boron leads to blue diamonds. Other elements or structural anomalies within the crystal lattice can produce a wide spectrum of colors.
Inclusions, which are internal flaws, also contribute to the overall appearance. These can be mineral crystals, fluid pockets, or structural imperfections trapped within the diamond during its growth. The type, size, and location of these inclusions determine a rough diamond’s clarity and how transparent or opaque it appears.