Some of the first knives were ceramic or at least not metallic. Obsidian is sort of glass-like or ceramic-like. I would think that they would be great for skinning and such. Maybe not so good for chopping maple.
Obsidian is a glass-like volcanic rock that can be knapped into blades that are wickedly sharp. The Aztecs used obsidian knives, and a particularly nasty club embedded with obsidian blades.
Today Obsidian is used in cardiac scalpels, since the structure allows for a sharper and thinner blade than is possible with steel.
It's some cool stuff.
