Not to scale: in reality the magma chamber is a few km down, metamorphic rock typically forms 10–30 km deep, and each step takes thousands to millions of years.
The solid arrows show the main loop; the dashed arrows are shortcuts. Any rock can become any other type. Tap an arrow or a box.
The rock cycle is driven by two energy sources: the Sun (weather, water and ice break rock down and move it) and the Earth's internal heat (melting, metamorphism and moving plates), with gravity pulling sediment downhill.
This is the rock cycle diagram you draw and label in a test. Switch between the labeled diagram, a blank one to test your memory, and a quiz where you place each label yourself. You can also download both versions or print a label worksheet.
Tap a word, then tap the numbered box it belongs to (on the diagram or in the list below). Tap a filled box to take the word back. On a phone, swipe the diagram sideways to see every number.
Tap a rock to see how it formed and how to recognise it. Pictures are drawn to show the typical texture.
Tap a rock, then tap the box it belongs in. Tap Check when all nine are placed.
Igneous rock forms when molten rock cools and crystallizes. Sedimentary rock forms from layers of sediment that are pressed and cemented together. Metamorphic rock forms when existing rock is changed by heat and pressure without melting.
At the surface, weathering breaks rock down and erosion carries the pieces away; rivers deposit them in layers. Buried layers undergo compaction and cementation. Deep underground, heat and pressure cause metamorphism, and if it gets hot enough the rock melts. Magma cools and crystallizes, and uplift brings deep rocks back to the surface.
Magma that cools slowly deep underground (intrusive) grows large crystals, like granite. Lava that cools quickly at the surface (extrusive) gets tiny crystals, like basalt, or none at all, like obsidian glass. (Granite and basalt also differ in their minerals: the fast-cooled version of granite magma is rhyolite.) Geologists use clues like this, along with layers, fossils and bands, to read a rock's history.
Press A rock's journey a few times: every trip is different, because the rock cycle has many paths. Then try Cooling underground and Eruption and compare where each igneous rock forms. Finally, sort the 12 rocks and label the diagram.
| Type | How it forms | Clues to spot it | Examples |
|---|---|---|---|
| Igneous: intrusive | Magma cools slowly underground | Large interlocking crystals | Granite, gabbro, diorite |
| Igneous: extrusive | Lava cools quickly at the surface | Tiny crystals, glassy, or gas holes | Basalt, obsidian, pumice, rhyolite |
| Sedimentary: clastic | Pieces of rock compacted and cemented | Grains, layers, sometimes fossils | Sandstone, shale, conglomerate |
| Sedimentary: chemical / biological | Minerals settle out of water, or shells and plants pile up | Fossils, fizzes in acid (limestone) | Limestone, chalk, rock salt, coal |
| Metamorphic: foliated | Heat and squeezing from one direction line minerals up in layers | Bands or thin sheets | Slate, schist, gneiss |
| Metamorphic: non-foliated | Heat and pressure re-crystallize one main mineral | No bands, sugary crystals | Marble, quartzite |
| Parent rock | Metamorphic rock |
|---|---|
| Shale | Slate → schist → gneiss (with more and more heat and pressure) |
| Limestone | Marble |
| Sandstone | Quartzite |
| Granite | Gneiss |
Two sources of energy: the Sun, which powers the weather and the water cycle that break rock down and move it, and the Earth's internal heat, which melts rock and moves the tectonic plates that bury rock, squeeze it into mountains and lift it up again. Gravity pulls sediment downhill and compacts buried layers. Plate tectonics links it all: at plate boundaries, rocks are buried, melted, erupted and uplifted.
| Process | Typical time |
|---|---|
| Lava cooling into basalt | hours to decades |
| Weathering and erosion of a mountain | millions of years |
| Sediment becoming sedimentary rock | thousands to millions of years |
| Metamorphism | millions of years |
| A granite intrusion cooling | thousands to millions of years |
| Uplift into mountains | millions of years (a few mm per year) |
The Earth is about 4.5 billion years old; the oldest known rocks, in northern Canada, are about 4 billion years old, and some mineral grains in Australia are about 4.4 billion years old.
The rock cycle is the never-ending process by which rocks change from one type to another over millions of years. Weathering and erosion break rock into sediment, sediment becomes sedimentary rock, heat and pressure make metamorphic rock, melting makes magma, and magma cools into igneous rock, which can start the cycle again.
Key takeaway: rocks are recycled into new rocks over millions of years.Igneous rock forms when magma or lava cools (granite, basalt). Sedimentary rock forms from layers of sediment pressed and cemented together (sandstone, limestone, shale). Metamorphic rock forms when rock is changed by heat and pressure without melting (marble, slate, gneiss).
Key takeaway: igneous = cooled melt; sedimentary = layers; metamorphic = changed by heat and pressure.Energy from the Sun drives weathering and erosion through the weather and the water cycle. The Earth’s internal heat drives melting, metamorphism and the movement of tectonic plates that bury and uplift rock. Gravity moves sediment downhill and squeezes buried layers.
Key takeaway: the Sun on the outside, the Earth’s heat on the inside.Both are molten rock. Magma is underground; lava is magma that has reached the surface through a volcano. Magma cools slowly into intrusive igneous rock with big crystals; lava cools quickly into extrusive rock with small crystals or glass.
Key takeaway: same melt: magma below, lava above.Sediment settles in layers, one on top of another, usually in water. Plants and animals that die can be buried in the layers before they rot, and later turn into fossils. Igneous rocks form from melt, so they do not contain fossils; the heating and squeezing that make metamorphic rocks usually destroy them.
Key takeaway: layers of sediment can bury and preserve living things.Most steps take thousands to millions of years. Lava can cool into rock in hours, but wearing down a mountain, turning sediment into rock or forming metamorphic rock takes millions of years. A full trip around the cycle can take hundreds of millions of years.
Key takeaway: very slow: thousands to millions of years per step.No. There are many paths. Igneous rock can be weathered into sediment, changed into metamorphic rock or melted again; sedimentary rock can be weathered or metamorphosed; metamorphic rock can be uplifted and weathered or melted. Try "A rock’s journey" in the 3D lab to see random paths.
Key takeaway: any rock can become any other type.Look at the texture. Igneous rocks have interlocking crystals or are glassy, sometimes with gas holes. Sedimentary rocks have grains or pebbles cemented together, often layers and fossils. Metamorphic rocks often have bands or thin sheets (foliation) or sugary, tightly packed crystals.
Key takeaway: crystals or glass = igneous; grains and layers = sedimentary; bands = metamorphic.