I have some nice chunks of obsidian that I picked up out west. In 75 years of headhunting I’ve never come across so much as a single flake of obsidian here on the East Coast. I know that stuff flakes extremely well. I can easily chip a surgical blade from my biggest chunk (from Mexico). It will slice through a sheet of newspaper as well as any razor blade you can buy.
It used to be obsidian was used to make a specific brain surgery implement, nothing else on earth can be made as sharp, so that’s what they used.