Ancient Obsidian Blades used by Aztecs are 500 times sharper than the sharpest steel.
Blade edges made out of obsidian are so sharp that they don’t seem jagged even when seen under an electron microscope. Their edges, if made carefully using processes like pressure flaking process, can get up to 3 nm thick. Good quality blades can make cuts down to single molecules! That is about 500 times sharper than the sharpest steel blade.
Top Image : Here is a highly magnified image (using a scanning electron microscope) of two strands of hair. The left one was cut using a fixed blade and the right one was cut using an electric razor.
Bottom Image : Left: Obsidian tip under and electron microscope. Right: Steel point under an electron microscope.