Example 1
Molten rock cools slowly underground and develops large crystals. Name the rock category.
Igneous. Slow underground cooling often permits larger crystals.
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Year 8
Rock types and formation
Match igneous, sedimentary and metamorphic rocks to formation processes.
Method and worked examples
Igneous rock forms when molten material cools and solidifies. Magma is below the surface; lava reaches the surface. Slow cooling often allows larger crystals. Sedimentary rock commonly forms when deposited sediments are compacted and cemented, although chemical and biological formation pathways also occur.
Metamorphic rock forms when existing rock changes under heat, pressure or active fluids without complete melting. Melting followed by solidification instead produces igneous rock. A rock category describes formation, not simply location or colour. Later processes can change its category: igneous rock can weather into sediment or change directly into metamorphic rock.
Example 1
Example 2
Limestone changes under heat and pressure without melting to form marble. Name the change and final category.
Metamorphism produces a metamorphic rock; complete melting is not part of this stated process.
Watch out: Metamorphism changes existing solid rock. Melting followed by solidification forms igneous rock.