When hot lava erupts from volcanoes and cools rapidly, it creates a naturally forming volcanic glass known as Obsidian.
Because it has no crystal structure, obsidian blade edges can be extremely thin, making it the perfect material for tool making. In ancient times, obsidian was used for arrowheads. Today, this igneous rock is still used for making surgical scalpel blades.
When Mount Vesuvius erupted in Pompeii, the extreme heat from the volcanic explosion turned a man’s brain into obsidian glass. Scientists found intact neurons preserved as obsidian in the corpse of a poor victim, in probably the most gruesome example of what’s known as “vitrification”, which is when a liquid is cooled into a solid so quickly that crystals don't form.