Someone who perished in the Mount Vesuvius eruption of 79 CE had their brain turned to glass under a unique set of conditions, according to an Italian volcanologist at the University of Roma Tre.
The brain fossilized inside the person’s skull as dark-colored glass when an extremely hot yet brief ash cloud descended upon Herculaneum. Studying the ancient discovery brings to light hidden dangers on the edges of volcanic eruptions, providing an unsettling warning to modern humans.
A One-of-a-kind Discovery
“We found fragments. Many fragments but not the full brain,” lead author Guido Giordano, a professor of volcanology at the Department of Science at the University of Roma Tre, told The Debrief. “We envisage that the fast heating probably destroyed part of it but did not have enough time to fully vaporize the brain, leaving fragments available for the following fast cooling once the ash cloud dissipated.”
Naturally occurring glass is rare due to the specific and unlikely conditions under which it forms. The temperature difference between the substance transforming and its environment must be significant, and the substance must become solid at a temperature greater than its surroundings, allowing the hot liquid to cool into a solid form so quickly it doesn’t crystalize in the process. Organic glass is scarce, as water makes up a significant portion of organic matter, and the ambient temperatures in high heat events are rarely low enough for water to solidify.
Analyzing an Ancient Glass Brain
Giordano and his colleagues analyzed glass fragments from inside the skull and spinal cord of the body, which was discovered still lying in its bed in the Collegium Augustalium. They imaged the sample with X-rays and electron microscopy, finding that the brain must have achieved a temperature of at least 510° C before rapidly cooling. Amazingly, the glass fossilization preserved the brain tissue.
“The neural structures are amazingly preserved, and the paper contains excellent micro-images of those,” Giordano said.
The circumstances were particularly unusual. The pyroclastic flows that oozed down from Mount Vesuvius to cover Herculaneum only reached 465° C and cooled slowly. Comparing what Giordano’s team found to modern volcanology research, they identified a quickly dissipating but super-heated ash cloud as the first deadly event when the volcano erupted. As the body rapidly reached over 510° C, the skull and spine protected the brain from a complete thermal breakdown, allowing a unique glass to form with the rapid cooling.
Discovery at Mount Vesuvius
A paper published in 2020 was the first to identify the unique vitrified brain, although it did not identify the underlying process at that time. The site only contained a single individual who experienced this bizarre transformation.
“This is because conditions must have been very specific because the organic tissue must have experienced a heating fast enough not to entirely destroy it (which is instead the most common occurrence for all other excavated skeletons) and then fast cool to turn into glass,” Giordano explained. “I suspect that the building and the room where the body was discovered offered those right conditions, so while possible, I think it is unlikely.”
“I know that similar occurrences have been described in the case of Hiroshima, but I have not found specific studies,” Giordano added.
Lessons from One of the Ancient World’s Deadliest Eruptions
“Let me say that our study bears a great lesson for the present. In active volcanic areas, while it is essential to evacuate all people, possibly in the way of pyroclastic flows, it is also essential to fit houses as shelters able to resist heat, such as it is done for wildfires,” Giordano concluded.
This way, should anyone be caught in a dilute hot ash cloud, there could be a possibility to survive and wait for rescue,” he said.
The paper “Unique Formation of Organic Glass from a Human Brain in the Vesuvius Eruption of 79 CE” appeared on February 27, 2025, in Scientific Reports.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.