system
Given the following post, respond as if you're commenting on Reddit:
human
How can obsidian be more smooth and sharp than honed steel?

I understand that it is glass, and something like steel is a somewhat crystalline, ordered structure. Please correct me if I'm wrong, but my current level of understanding makes the idea of glass being sharper than metal seem...well, backwards.
gpt
Steel is almost always composed of very many separate crystals, rather than one large one.  
When steel fractures, it typically fractures along the uneven joins between septate crystals.   
Obsidian contains almost no crystals large enough to affect the material's fracture properties and it is for this reason it breaks smoothly and sharply. Because obsidian lacks crystals, it does not break along lines of weakness in the material, it just fractures along the lines of the stress that caused the fracture. This is also why obsidian and similar materials show conchoidal fractures.  
When you look at the shape of some fractured obsidian, you are looking at the shape of the shockwave that cracked it. When you look at the shape of some fractured steel, you are looking partly at the shape of the shockwave that fractured it, but mostly at the lines of weakness between the steel's imperfections and the joins between it's crystals.