Video narration
How can the little stone you pick up on a walk become a different kind of rock? It looks fixed, but its story depends on how it formed-and what happens next. Igneous rocks form when melted rock-magma underground or lava at the surface-cools and hardens; granite and basalt are examples. Sedimentary rocks form as bits build up in layers, then get pressed and stuck together, like sandstone and limestone. Metamorphic rocks are older rocks changed by intense heat and pressure. Marble and slate are examples. Those names describe how a rock forms, not where its story ends. Limestone can become marble, shale can become slate, and granite can become gneiss. These are possible changes, not a route every rock follows. Different processes let rocks change kind again and again. That ongoing change is the rock cycle.