Obsidian

volcano · glass · igneous rock

Volcanic glass formed. Obsidian is created when hot lava shoots out of a volcano and cools down really quickly, before it has time to turn into crystals.

Smooth and glassy. Because the lava cools so fast, atoms don't have time to rearrange themselves into crystal patterns, so obsidian ends up smooth and shiny like glass instead of rocky and bumpy.

Rich in light elements. Obsidian comes from a special type of lava called felsic lava that's packed with lighter elements like silicon, oxygen, and aluminum.

Usually dark colored. Most obsidian is black or dark gray, and it looks almost like polished stone or dark glass when you hold it up to the light.

Found in lava flows. Obsidian is commonly discovered along the edges of thick, slow-moving lava flows called rhyolitic flows that had so much silica they couldn't flow easily.