Raw diamonds are uncut, unpolished gems found in their natural state. Unlike faceted jewelry stones, they often have a rough exterior and may resemble ordinary rocks or pebbles. They retain their original crystalline structure, commonly appearing as octahedrons or dodecahedrons.
Kimberlite Pipes: Primary Sources
Kimberlite pipes are the most significant primary source for raw diamonds. These deep volcanic conduits originate from the Earth’s mantle, at depths ranging from 93 to 280 miles (150 to 450 kilometers). Intense heat and pressure cause carbon atoms to fuse into diamonds’ crystalline structure. These formations are composed of kimberlite, a dark-colored, heavy igneous rock often with a bluish or greenish hue.
Kimberlite pipes are characterized by their distinctive carrot-like shape, tapering downward. Magma within these pipes acts as a rapid elevator, transporting diamonds from the mantle to the surface in hours. This rapid ascent is crucial; prolonged exposure to magma could transform their crystalline structure back into graphite. Diamonds found within these pipes are considered primary sources, as they are still embedded in their original geological matrix.
Alluvial Deposits: Secondary Sources
Alluvial deposits are a significant secondary source of raw diamonds. These deposits form when diamonds erode from their primary kimberlite sources over millions of years. Natural forces like rivers, glaciers, and wind transport these liberated diamonds to new locations. Diamonds settle in these new environments based on their weight and density, often concentrating in specific areas.
Common locations for alluvial deposits include riverbeds, ancient river channels, and coastal areas, sometimes extending to offshore seabeds. Alluvial diamonds often appear more rounded or worn due to transportation. Recovery methods range from traditional panning and sieving to mechanized dredging. These diamonds are often of good quality, as weaker stones may not survive the journey.
Global Distribution of Discoveries
Raw diamonds are globally distributed, with significant discoveries across several continents. Russia is a leading producer, with most diamonds originating from kimberlite pipes in Siberia’s Yakutia region. Botswana, a major African producer, also derives most diamonds from kimberlite pipes, including notable mines like Orapa and Jwaneng. South Africa, where kimberlite pipes were first identified, continues to have both primary kimberlite and historical alluvial sources, particularly along its Atlantic coast.
Canada has emerged as a significant producer, with diamond-bearing kimberlite pipes in its remote northern territories. Australia, known for its Argyle mine, produced diamonds from both kimberlite and lamproite pipes, though its production has declined. Other countries like Angola, Namibia, and the Democratic Republic of Congo have substantial alluvial diamond deposits, often in riverbeds and coastal areas. Historically, India and Brazil were prominent sources, primarily from alluvial deposits.
Rare and Extraterrestrial Origins
Beyond traditional geological formations, raw diamonds can also be found in rare and scientifically interesting settings. Impact craters, for example, where extreme pressure and temperature from a meteorite strike transform carbon-rich rocks into diamonds. Russia’s Popigai crater, formed by an asteroid impact 35 million years ago, contains an estimated trillions of carats of these “impact diamonds.” These diamonds are often microscopic, polycrystalline, and more suitable for industrial applications than for jewelry.
Diamonds also exist beyond Earth, with microscopic diamonds discovered in meteorites. These extraterrestrial diamonds, sometimes called nanodiamonds, can originate from ancient cosmic collisions or within stars before our solar system formed. Some meteorites, such as ureilites, contain lonsdaleite, a rare diamond with a hexagonal crystal structure theorized to be harder than regular diamonds. While not commercially viable for gem production, these sources offer insights into diamond formation under unique cosmic conditions.