A deadly ash cloud preserved the man's brain as glass for thousands of years.

In a nutshell Scientists discovered a human brain from 79 CE Vesuvius eruption transformed into glass—the only known case of natural organic glass preservation in history. The brain vitrified at temperatures above 510°C followed by extremely rapid cooling,

It was a surprising discovery when scientists examining the remains of a man who died in bed in the ancient city of Herculaneum after Italy's Mount Vesuvius erupted in 79 AD found dark fragments resembling obsidian inside his skull.