Jonny Crockett answers a question on obsidian rock

Question: I’ve been told about a material called Obsidian being made into a knife so sharp that it’s sharper than a surgeon’s scalpel. Is this true?

Jonny Crockett replies: The answer to this is yes, it is true. Obsidian forms when lava cools rapidly with as little crystal growth as possible as a result. When cleaved, Obsidian can produce an edge that is one molecule thick. When viewed under a microscope you can see it has a perfectly straight edge. When you view a scalpel under a microscope it looks like a saw with hundreds of teeth. I found some at the top of Kilimanjaro and tried to bring it back with me but it got lost in transit. It comes in various colours but is more commonly black, though some is a deep red colour. You can buy Obsidian knives, but they are extremely expensive and very brittle. They are lovely to use though!