Igneous rock — Science definition
Rock that forms when molten magma or lava cools and hardens (crystallizes).
Where it is taught
- The Three Rock Types — Rocks, Landscapes & Water, Earth & Space Science, Grade 9
Questions using igneous rock
Problem 1
Explain why obsidian (volcanic glass) has essentially no visible crystals at all, even though it's an igneous rock.
Answer and explanation
Obsidian forms when lava cools extremely fast at Earth's surface, so its atoms have almost no time to arrange into ordered crystal structures at all.