Back to: Natural Diamonds & Sustainability
Diamonds, often referred to as the “king of gems,” have captivated humanity’s imagination for centuries. These precious gemstones are not only valued for their beauty and durability but also for their fascinating geological origins. To understand the geology of diamonds, we must delve into the depths of the Earth’s mantle, where these gems are formed over billions of years.
The Earth’s Mantle: A Crucible for Diamond Formation
The Earth’s mantle is a vast layer located between the thin crust and the core of our planet. Composed mainly of solid rock, the mantle experiences immense pressure and temperatures reaching over a thousand degrees Celsius. This extreme environment provides the necessary conditions for diamond formation.
Carbon: The Building Block of Diamonds
Diamonds are essentially carbon crystals. However, the specific carbon atoms that form diamonds are distinct from those found in other minerals or even graphite. Diamonds result from carbon atoms arranging themselves in a crystal lattice structure under intense heat and pressure.
Formation Process: From Ancient Volcanoes to Kimberlite Pipes
Diamonds are typically formed deep within the Earth, around 150 to 200 kilometers below the surface. The formation process begins with carbon-rich materials, such as organic matter or carbonates, being subducted into the mantle through tectonic activity.
Over time, these carbonaceous materials are subjected to high temperatures and pressures, causing chemical reactions that release carbon atoms. These carbon atoms then bond together to form diamond crystals within pockets of magma.
Subsequently, volcanic eruptions propel these diamond-bearing rocks, known as kimberlite or lamproite, toward the Earth’s surface. The explosive nature of these eruptions, combined with the magma’s rapid ascent, allows the diamonds to survive the journey without undergoing transformations that would destroy them.
Kimberlite Pipes: Diamond Delivery Channels
Kimberlite pipes are vertical conduits that transport diamond-bearing rocks from the mantle to the Earth’s surface. These pipes are the result of ancient volcanic activity and serve as primary sources of diamonds worldwide.
Once the volcanic material reaches the surface, it often forms cone-shaped deposits called volcanic craters or “diatremes.” These structures are rich in various minerals, including diamonds.
The Journey to the Surface and Diamond Mining
The natural erosion processes, such as weathering and river activity, gradually expose these kimberlite pipes at the Earth’s surface. Miners identify potential diamond deposits by analyzing the geological characteristics associated with these volcanic pipes.
Modern diamond mining involves both open-pit and underground methods. In open-pit mining, the surface layers are removed to access the diamond-rich kimberlite pipes below. Underground mining, on the other hand, involves tunnelling beneath the surface to extract the valuable rocks.
Conclusion
The geology of diamonds is a remarkable tale of extreme pressures, high temperatures, and ancient volcanic activity. These gemstones, with their captivating beauty and rarity, endure a unique journey from the Earth’s mantle to become the treasures we cherish. Understanding the geological processes behind diamond formation enhances our appreciation for these fascinating creations of nature.