Diamonds Are Not Made from Coal
Contrary to popular belief, diamonds are rarely formed from coal. Most diamonds are billions of years older than the first land plants that created coal.
About this fact
The idea that diamonds come from coal is one of the most persistent geological myths. In reality, most diamonds formed deep in the Earth's mantle 1-3.5 billion years ago, long before plants existed on land to create coal (which formed 300-360 million years ago). Diamonds form from carbon under extreme pressure and temperature conditions about 150-200 kilometers below the surface. The carbon sources are typically carbonate rocks, organic carbon in subducted oceanic crust, or primordial carbon from the Earth's formation. While it's theoretically possible for coal to become diamond under the right conditions, this almost never happens naturally. The rare exceptions require very specific geological circumstances involving coal seams being subjected to extreme pressure during mountain formation.