An obsidian blade can terminate in an edge roughly three nanometres wide. A surgical steel scalpel, honed to its practical limit, stops near 500. The difference is not craftsmanship. It is the absence of structure. Obsidian is volcanic glass. Rhyolitic lava at 70 to 75 percent silica, so viscous and so rapidly quenched that the silicon-oxygen tetrahedra never organise into a lattice. No grains. No crystal boundaries. No preferred cleavage planes. It is frozen liquid, isotropic all the way down. That matters because a metal edge is limited by its own microstructure. Steel is a mosaic of grains and carbide particles, and the finished edge can never be finer than the features it is built from. Grind past that limit and the carbides tear out, leaving a ragged, serrated line under an electron microscope. Glass has nothing to tear out. Fracture it correctly and the crack front propagates through a continuum, terminating in an edge only a few molecular layers thick. The mechanism is conch...