“Diamonds are made from compressed coal”

The idea that diamonds are simply compressed coal is a widely held belief, but it's a misconception. While both substances are primarily composed of carbon, their origins and formation processes are vastly different. The vast majority of natural diamonds formed deep within the Earth's mantle, typically 150 to 250 kilometers (93 to 155 miles) below the surface, under immense pressure and temperatures exceeding 1,000 degrees Celsius. These conditions existed long before land plants, the source material for coal, even appeared on Earth.

Scientific evidence clearly shows that most diamonds are incredibly ancient, with ages ranging from 1 billion to 3.5 billion years old. In contrast, coal began forming from decayed plant matter in swamps much later, around 300 to 450 million years ago, and typically at much shallower depths, rarely exceeding a few kilometers below the surface. The carbon in diamonds usually comes from primordial carbon trapped in the Earth's mantle or from carbon-bearing fluids, not from fossilized organic material like coal. Furthermore, coal seams are sedimentary rock layers, usually horizontal, while diamonds are brought to the surface in vertical igneous rock formations known as kimberlite pipes.

This common misconception likely stems from a few factors. Both diamonds and coal are carbon-based and form underground under significant heat and pressure, leading to a superficial association. The motivational saying, "a diamond is a chunk of coal that did well under pressure," also perpetuates this inaccurate idea. Additionally, popular culture, such as depictions of fictional characters like Superman squeezing coal into diamonds, has cemented this myth in the public consciousness.