When you think of diamonds, you might imagine glittering jewelry, extravagant proposals, or even Hollywood red carpets. But behind every diamond lies a fascinating geological journey, one that begins deep beneath Earth’s surface—in a rock called kimberlite.
What is Kimberlite ?
Kimberlite isn’t just any rock. It’s a rare, volcanic rock that acts as a delivery system for one of Earth’s most precious materials: diamonds. Found mostly in old, stable parts of the Earth’s crust known as cratons, kimberlite forms from magma that originates over 150 kilometers (about 90 miles) deep, in the mantle—that scorching layer beneath the crust.
What makes kimberlite so unique isn’t just its deep origin. It’s the explosive way it travels to the surface. Kimberlite eruptions are like geological rockets. The magma moves so quickly—sometimes at supersonic speeds—that it brings with it materials from the mantle, including diamonds that formed under extreme pressure and temperature.
How Are Diamonds Formed?
Before diamonds ever meet kimberlite, their story starts in the mantle, under crushing pressure and temperatures exceeding 1000°C (1832°F). Under these extreme conditions, carbon atoms bond in a unique crystal structure that results in a diamond.
But here’s the catch: if diamonds stay in the mantle, they’re inaccessible. And if they rise too slowly to the surface, they may turn into graphite (the stuff in your pencil) due to changing temperature and pressure. So they need a speedy escape route—this is where kimberlite swoops in like a geological superhero.
The Explosive Journey of Kimberlite Magma
Kimberlite magma forms deep in the mantle and contains volatile elements like carbon dioxide and water, which make it incredibly buoyant and explosive. When it starts rising, it races toward the surface through cracks and weaknesses in the Earth’s crust.
During its journey, it tears off pieces of the mantle, crust, and anything in its way. These fragments, known as xenoliths, provide clues about the deep Earth. When it finally reaches the surface, the magma erupts explosively, creating vertical pipe-like structures called kimberlite pipes—the primary sources of mined diamonds.
These eruptions are so fast and violent that they’re over in a matter of hours, leaving behind crater-like features and a vertical pipe filled with broken rock, ash, and, if you’re lucky, diamonds.
Kimberlite Pipes: The Diamond Hotspots
Not all kimberlite pipes contain diamonds, and not all diamonds in them are economically valuable. But some pipes—like those found in South Africa, Russia, Canada, and Australia—have produced millions of carats.
One of the most famous kimberlite sources is the Big Hole in Kimberley, South Africa, which sparked the diamond rush in the late 1800s. The discovery of diamond-bearing kimberlite here changed the world’s diamond industry forever.
Modern mining now focuses on pipes that are rich in diamonds and easy to access. Geologists use satellite imaging, soil geochemistry, and geophysical surveys to locate hidden kimberlite pipes.
What Else Is in Kimberlite?
Diamonds might be the stars, but kimberlite has its own supporting cast. It often contains minerals like:
- Olivine – A green, glassy mineral from the mantle.
- Phlogopite – A shiny mica that gives clues about the magma’s chemistry.
- Ilmenite and Chromite – Indicator minerals that geologists track to find kimberlite.
- Garnet (especially G10 garnets) – Their presence is often linked with diamond potential.
By studying these minerals, geologists can predict whether a kimberlite is likely to host diamonds, even before any digging begins.
The Global Hunt for Kimberlite
Finding kimberlite is like searching for buried treasure. Since many pipes are buried under soil, forests, or even ice, exploration involves some pretty advanced science.
In Canada’s Northwest Territories, diamond-bearing kimberlite pipes were found under lakes and tundra using aeromagnetic surveys—where planes fly over land and detect magnetic anomalies caused by the iron-rich minerals in kimberlite.
In Botswana, exploration teams follow trails of indicator minerals like garnet and chrome diopside back to their source. These minerals are often more widespread than diamonds themselves and act like breadcrumbs leading to the motherlode.
Kimberlite vs. Lamproite
While kimberlite gets most of the fame, it’s not the only rock that can host diamonds. Lamproite, another volcanic rock, has also delivered diamonds to the surface. The Argyle Mine in Western Australia, famous for its rare pink diamonds, is actually hosted in lamproite.
Lamproite magmas form slightly differently, often in areas with more complex tectonic histories. But just like kimberlite, they erupt quickly and bring deep-mantle materials to the surface.
Are All Diamonds from Kimberlite?
Nope! Some diamonds come from alluvial deposits—where erosion carries diamonds from their original kimberlite pipe into rivers or coastal sands. These diamonds may have traveled miles from their source, worn smooth by time and water.
These alluvial diamonds are often easier to mine and have been historically significant, especially in countries like Sierra Leone, Angola, and Brazil.