Obsidian has been used in cardiac surgery , as well-crafted obsidian blades have a cutting edge many times sharper than high-quality steel surgical scalpels , with the edge of the blade being only about NUMBER@1 nanometres wide .

Obsidian is used in heart surgery , as well-crafted obsidian blades have a cutting edge many times sharper than high-quality steel surgical scalpels , with the edge of the blade being only about NUMBER@1 nm wide .
