“Diamonds are formed from compressed coal”

The widespread notion that diamonds are merely chunks of coal compressed under immense pressure is a persistent misconception, often fueled by popular culture and a simplified understanding of geology. This myth likely stems from the fact that both diamonds and coal are primarily composed of carbon and are found deep within the Earth. The appealing narrative of an ordinary substance transforming into something extraordinary under stress has also contributed to its longevity, with sayings like "a diamond is a chunk of coal that did well under pressure" becoming common idioms. Furthermore, fictional portrayals, such as Superman (Review) squeezing coal into diamonds, have cemented this inaccurate idea in the public consciousness.

However, the scientific reality of diamond formation tells a far more ancient and profound story. Natural diamonds originate deep within the Earth's mantle, typically 100 to 250 miles below the surface, where temperatures soar above 2,000°F and pressures are staggeringly intense. Under these extreme conditions, pure carbon atoms crystallize over millions, even billions, of years into the robust structure of a diamond. These precious gems are then brought closer to the surface through rare, deep-seated volcanic eruptions, carried within igneous rocks known as kimberlite pipes.

In stark contrast, coal forms much closer to the Earth's surface, usually within a few miles deep, from the decayed remains of ancient land plants. The critical piece of evidence debunking the coal-to-diamond myth lies in their respective ages. Most natural diamonds are between 1 billion and 3.5 billion years old, predating the existence of land plants, which first appeared on Earth about 450 million years ago. This significant age difference, coupled with the vastly different geological environments and carbon sources, confirms that coal has rarely, if ever, played a role in the formation of commercial diamonds.