Diamonds are revered for their brilliance and durability. Many associate their formation with intense geological processes deep within the Earth. This article explores the science behind diamond creation, clarifying common beliefs.
The Common Misconception
A widespread belief suggests natural diamonds form directly from coal. This idea stems from both being carbon-based materials found underground. However, this popular notion does not align with geological realities, as their formation conditions are vastly different.
How Natural Diamonds Really Form
Natural diamonds typically form deep within the Earth’s mantle, 90 to 120 miles (145 to 190 kilometers) below the surface. This process requires extreme conditions: temperatures from 900 to 1,300 degrees Celsius (1,652 to 2,372 degrees Fahrenheit) and immense pressures of 45,000 to 60,000 atmospheres. These conditions cause carbon atoms to crystallize into the unique structure that gives diamonds their hardness.
The carbon source for these diamonds is usually deep carbon from the Earth’s mantle or recycled carbon from subducted oceanic plates, not coal. These carbon-rich fluids transform under intense heat and pressure over millions or billions of years. Once formed, diamonds are brought to the surface through rapid volcanic eruptions, creating vertical channels of igneous rock known as kimberlite and lamproite pipes.
How Coal Really Forms
Coal, in contrast to diamonds, forms from the remains of ancient plant matter. This process begins in swampy wetlands where dead vegetation accumulates faster than it can fully decompose. Over millions of years, these layers are buried under sediment, subjecting them to heat and pressure.
The transformation into coal, known as coalification, involves stages such as peat, lignite, and anthracite. These stages represent increasing carbon content and density, occurring under significantly less extreme conditions than diamond formation. Coal deposits are typically found much closer to the Earth’s surface, within 2 to 3 miles (3.2 kilometers) deep, in sedimentary layers. This shallow origin distinguishes coal formation from the deep geological processes that create natural diamonds.
Man-Made Diamonds
Diamonds can also be created by humans in controlled laboratory environments. These man-made diamonds are produced for both industrial applications and jewelry, sharing the same chemical, physical, and optical properties as natural diamonds.
Two primary methods are used: High-Pressure/High-Temperature (HPHT) and Chemical Vapor Deposition (CVD). The HPHT method mimics natural conditions, using a carbon source like graphite to grow diamonds around a small seed. The CVD method involves placing a diamond seed in a vacuum chamber filled with carbon-rich gases, which break down and deposit carbon atoms layer by layer. Both techniques produce real diamonds from carbon, but neither uses coal as their direct carbon source, and their creation occurs rapidly.