Earth-mined diamonds are naturally occurring minerals composed primarily of carbon. They form deep within the Earth’s mantle over immense timescales. Their natural origin distinguishes them from laboratory-created diamonds. Each earth-mined diamond possesses a unique structure, reflecting its individual journey within the Earth.
Geological Formation
Earth-mined diamonds originate 100 to 200 kilometers below the Earth’s surface, within the mantle. Here, carbon atoms are subjected to extreme conditions, including temperatures from 900 to 1300°C and pressures between 45 to 60 kilobars (over 45,000 times atmospheric pressure). This intense environment causes carbon atoms to bond into the rigid, tetrahedral crystal lattice structure characteristic of diamonds. This formation process typically spans one billion to 3.3 billion years.
Diamonds journey to the Earth’s surface through deep-seated volcanic eruptions. Molten rock, known as kimberlite or lamproite magma, rises rapidly through cracks in the Earth’s crust, forming vertical structures called pipes. These eruptions bring diamonds from the mantle to shallower depths. The quick ascent prevents diamonds from transforming into graphite due to changes in pressure and temperature.
Mining and Recovery
Earth-mined diamonds are extracted from two primary deposit types. Primary deposits are found within kimberlite and lamproite pipes, the volcanic conduits that brought diamonds to the surface. Secondary, or alluvial, deposits form when diamonds erode from these pipes and are transported by natural forces like rivers and ocean currents, accumulating in gravel beds or coastlines.
Mining methods vary by deposit type and depth. Open-pit mining removes overlying rock to expose diamond-bearing kimberlite in surface deposits. For deeper deposits, underground mining excavates shafts and tunnels to reach the ore. Marine mining, using specialized vessels, extracts diamonds from the seabed in coastal areas.
After collection, the diamond-bearing ore undergoes processing steps. These include crushing to reduce rock size, scrubbing and screening to remove loose material, and dense media separation, where diamonds sink due to their high density. X-ray luminescence is then used to separate diamonds from other minerals.
Key Characteristics
Earth-mined diamonds exhibit inherent qualities that contribute to their unique appearance and value. Color ranges from colorless to “fancy” colors like yellow, blue, pink, and green. Trace elements incorporated during formation, such as nitrogen (yellow) or boron (blue), influence these variations. Pink diamonds often derive their color from crystal lattice distortions caused by heat and pressure after formation.
Clarity refers to the presence of internal inclusions and external blemishes. Inclusions are internal characteristics like tiny crystals or small cracks, while blemishes are surface imperfections. These are evaluated based on their size, number, location, and visibility under 10x magnification.
The crystal shape of a rough diamond, typically an octahedron, influences how it can be cut to maximize brilliance. Carat weight is the standard unit of measurement for a diamond’s mass, with one carat equaling 0.2 grams. It is often incorrectly associated directly with physical size.
Certification and Identification
Independent gemological laboratories verify the natural origin and quality of earth-mined diamonds. Organizations like the Gemological Institute of America (GIA), International Gemological Institute (IGI), and American Gem Society (AGS) evaluate and certify these stones. A certification report typically confirms the diamond’s natural origin and provides a detailed assessment of its characteristics, including color, clarity, cut, and carat weight.
Laboratories use advanced scientific methods to distinguish natural diamonds from laboratory-grown diamonds or simulants. Techniques like spectroscopy, which analyzes light absorption patterns, and the examination of growth patterns and luminescence, help identify their unique formation signatures. Natural diamonds often contain trace amounts of nitrogen, a key differentiator from many lab-grown diamonds. The comprehensive evaluation and documentation provided by these certifications are important for consumer confidence and transparency in the diamond market.