Diamonds form when coal gets squeezed hard enough, deep underground
Both are forms of carbon, and the story that one simply compresses into the other is a staple of school science lessons. Does the geology actually back it up?
Myth or fact? Reveal
Myth. It's a myth. Most diamonds are older than Earth's first land plants — the source material for coal — and they form over 150km down in the mantle, far deeper than any coal seam, from carbon that predates life on land entirely.