Rock Cycle Diagram: Interactive 2D and 3D

What is the rock cycle?

Rocks look like they never change, but they do. Over thousands to millions of years, every rock on Earth is slowly being broken down, buried, squeezed, heated, melted and made into new rock. The rock cycle is the name for all of those changes together. National Geographic describes it as a series of processes that create and transform the types of rocks in Earth's crust.

There are three main types of rock, and the rock cycle explains how each one can turn into the others:

• Igneous rock forms when melted rock cools and hardens.
• Sedimentary rock forms when layers of sediment are pressed and glued together.
• Metamorphic rock forms when heat and pressure change an existing rock without melting it.

The interactive diagram above shows the five stages (magma, igneous rock, sediment, sedimentary rock and metamorphic rock) and the five processes on the arrows between them. Tap any numbered pin to see what it means, then test yourself with the label and order quizzes.

The three types of rock

Steps of the rock cycle in order

The main loop in the diagram goes like this. Use it to practice the Order it quiz.

1. Magma. Deep underground, rock gets hot enough to melt. Melted rock rises and can collect in a magma chamber beneath a volcano.
2. Cooling and crystallization. Magma cools underground, or erupts as lava and cools at the surface. Minerals form crystals and the rock becomes solid.
3. Igneous rock. The new rock might be granite (cooled slowly underground) or basalt (cooled quickly from lava).
4. Weathering and erosion. Rain, ice, wind, plant roots and temperature changes crack rock into pieces. Rivers, wind, glaciers and gravity carry the pieces away.
5. Sediment. When moving water slows down, it drops its load. Sand, mud and pebbles settle in layers at the bottom of lakes and oceans. Dropping sediment is called deposition.
6. Compaction and cementation. New layers bury old ones. The weight squeezes out water, and dissolved minerals glue the grains together.
7. Sedimentary rock. The layers are now solid rock, such as sandstone or shale.
8. Heat and pressure. When rock is buried deep, or caught where tectonic plates collide, it is heated and squeezed. Its minerals rearrange without melting.
9. Metamorphic rock. Shale can become slate, and limestone can become marble.
10. Melting. Pushed deeper still, the rock can melt into magma, and the cycle continues.

Igneous rock: cooled from fire

The word igneous comes from the Latin word for fire. The USGS explains that igneous rocks form when hot, molten rock crystallizes and solidifies, and that the melting usually starts deep underground near active plate boundaries or hot spots.

Where the rock cools makes a big difference:

• Intrusive (plutonic) igneous rock cools slowly underground. Magma trapped deep inside the Earth can take thousands to millions of years to cool, so the crystals have time to grow large. Granite, diorite and gabbro are coarse-grained intrusive rocks.
• Extrusive (volcanic) igneous rock cools quickly at or near the surface. Lava hardens almost immediately in the cool air, so the crystals stay tiny. Basalt, andesite and rhyolite are fine-grained; obsidian cools so fast it becomes natural glass, and gas bubbles trapped in cooling lava leave holes like those in pumice.

A quick way to remember: big crystals mean slow, underground cooling; tiny or no crystals mean fast cooling at the surface.

Sedimentary rock: layers and fossils

Sedimentary rocks form from pieces of older rocks or from the remains of once-living things. The USGS notes that sediments usually travel in rivers and settle in lakes and oceans, and that when they are buried, they lose water and become cemented into rock. That is why sedimentary rock so often has layers, like the striped canyon walls and mesas of the desert Southwest.

There are three main kinds:

• Clastic rocks are made of broken pieces (clasts) of other rocks and are named by grain size.
• Biologic rocks form when huge numbers of living things die and pile up, as with some limestone and chert.
• Chemical rocks form when minerals settle straight out of water, as some limestone does.

Sedimentary rock is where fossils are found. According to the USGS, fossils are found almost exclusively in sedimentary rocks: igneous rocks are far too hot when they form, and the heat and pressure that make metamorphic rocks generally destroy fossil evidence. Plants and animals that die in or near water and are buried quickly by sediment have the best chance of being preserved.

Metamorphic rock: changed, not melted

Metamorphic means changed form. The USGS describes metamorphic rocks as rocks that started out as some other type and were substantially changed by intense heat, intense pressure, hot mineral-rich fluids, or a mix of these. Metamorphism does not melt the rock; if it did, the result would be magma and then igneous rock.

Pressure can line up flat minerals so the rock has stripes or sheets, called foliation. Rocks made of minerals that can't line up, like the calcite in limestone, become non-foliated rocks.

Marble is the famous one: it is the stone of countless statues and buildings, and it began as limestone.

Does the rock cycle have a beginning or an end?

No. The rock cycle is a loop, and rocks can take shortcuts. The dashed arrows in the diagram show two of them, but there are many more:

• An igneous rock can be squeezed into a metamorphic rock without ever being weathered.
• A metamorphic or sedimentary rock can be lifted to the surface and weathered into new sediment.
• Any rock type can melt into magma if it goes deep enough.

National Geographic puts it simply: any rock type can become any other. Most diagrams start with magma only because Earth's very first rocks formed from melted rock.

What drives the rock cycle?

Two sources of energy keep rocks moving through the cycle. Heat from inside the Earth melts rock, powers volcanoes, and moves the tectonic plates that bury rock, squeeze it into mountains and lift it back up. Energy from the Sun drives the weather and the water cycle, so rain, ice, wind and rivers can weather and erode the rock that reaches the surface. That is why a mountain range can be pushed up by plate collisions and worn down by rivers at the same time.

Who discovered the rock cycle?

The idea goes back to James Hutton, an 18th-century Scottish farmer, doctor and naturalist who is often called the founder of modern geology. Studying the rocks around Edinburgh and the Scottish coast, he argued that land is constantly worn away into the sea, buried and hardened into new rock, then pushed back up by heat from below. He presented these ideas to the Royal Society of Edinburgh, and they were published in 1788. His most famous line is that he found "no vestige of a beginning, no prospect of an end."

How long does the rock cycle take?

It depends on the step. Lava can harden in moments, and a flood can drop a layer of sediment overnight. Most of the cycle is far slower: magma deep underground can take thousands to millions of years to cool, and burying, compacting and changing rock usually takes millions of years. A single grain of sand might travel the whole loop many times over Earth's long history.

Explore the rock cycle in 3D

Select Open in 3D to see the same ten parts in a cutaway block of Earth's crust: a volcano fed by a glowing magma chamber, a mountain and river carrying sediment to the sea, layered sedimentary rock under the seafloor, and a folded metamorphic zone deep below. Drag to rotate, pinch or scroll to zoom, and tap any part for its explanation. The guided tour visits every stop in order with captions, and Play the cycle sends a pebble around the whole loop. If your device can't show 3D graphics, the page falls back to the 2D explorer, so every child can use it.

Rock cycle activities to try at home

• Rock hunt. Collect a few rocks on a walk and sort them: crystals (igneous?), layers or sand grains (sedimentary?), stripes or sparkles (metamorphic?).
• Crayon rock cycle. With an adult, shave old crayons into "sediment," press the shavings together in foil ("sedimentary"), warm and press them harder ("metamorphic"), then melt and cool them ("igneous"). Talk about which step each action stands for.
• Draw the cycle. After exploring the diagram, have your child draw it from memory, then check it against the labeled rock cycle diagram. For a test, print the rock cycle worksheet.

The rock cycle is a highlight of upper elementary and middle school earth science. If you want a full course that builds on it, compare the options in our best homeschool science curriculum guide or browse science programs, many of which families can pay for with a state scholarship or education savings account.