Rock Cycle

How to use it

In Be the rock you start out holding a piece of granite. Choose what happens to it next: melt it, cool the magma slowly underground or fast at the surface, weather and erode it, deposit and bury the sediment, squeeze and heat it, or uplift it. Only the processes that could really happen to your rock right now are switched on. Each step turns your rock into a real example, draws its texture, adds a line to your journey and traces your path on the rock cycle diagram. Try to visit all three rock types. Tap any station on the diagram to read about it.

Rock collection has cards for 13 common rocks, each with how it forms, a texture clue, a use and a Canadian place to see it. Filter by type, or press Hold this rock to start a journey from that rock. The Sorting quiz shows one rock at a time: decide whether it is igneous, sedimentary or metamorphic, then read why.

Igneous, sedimentary and metamorphic rock

Geologists sort rocks into three types by how they formed. Igneous rock forms when melted rock cools and hardens. Magma that cools slowly deep underground grows large crystals, like granite. Lava that cools quickly at the surface makes tiny crystals (basalt) or glass (obsidian). Sedimentary rock forms from sediment: weathering breaks rock into gravel, sand and mud, erosion carries the pieces away, and they settle in layers. Buried under more layers, they are pressed together (compaction) and glued by minerals (cementation). Limestone often forms from shells. Metamorphic rock forms when any rock is heated and squeezed deep underground until its minerals change, without melting. Shale becomes slate, limestone becomes marble, sandstone becomes quartzite and granite becomes gneiss.

The rock cycle has no fixed order. Any rock can be weathered into sediment once it is uplifted to the surface, any rock can melt, and a metamorphic rock can be changed again by more heat and pressure. Most steps take thousands to millions of years, which is why the rocks under our feet look so permanent. Lava is the big exception: it can harden in hours or days.

• Can a rock go from igneous to metamorphic without ever becoming sediment? Find the shortest path.
• Why does granite have big crystals but basalt has tiny ones?
• Collect rocks from the schoolyard and use the texture clues to sort them, then test for fizzing with a drop of vinegar.

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