Why does obsidian look like volcanic glass?

Obsidian is a natural volcanic glass, usually formed when silica-rich lava cools extremely quickly. Because atoms do not have time to organize into crystals, the rock solidifies in a disordered, glass-like state. This often happens at the edges of lava flows or when lava is quenched by water or air. Obsidian commonly breaks with sharp conchoidal fractures, which is why it was widely used for tools and blades in ancient cultures. Its glassy texture is a sign of rapid cooling, not melting into actual glass after the fact.