Rock Cycle
🪨 What Is the Rock Cycle?
The rock cycle is the continuous process that changes rocks from one type to another over time.
It shows how rocks are formed, broken down, and transformed by natural forces like heat, pressure, water, wind, and ice.
The three main types of rock are:
Igneous rock
Sedimentary rock
Metamorphic rock
🌋 Igneous Rocks
Igneous rocks form when magma (underground) or lava (above ground) cools and solidifies.
If magma cools beneath the Earth’s surface, it forms intrusive igneous rocks (e.g. granite).
If lava cools on the surface, it forms extrusive igneous rocks (e.g. basalt).
👉 These rocks often have crystals, depending on how slowly they cool.
🏞️ Sedimentary Rocks
Sedimentary rocks are formed when sediments (tiny pieces of rock, mineral, or organic material) accumulate in layers, get compacted and cemented over time.
Often formed in rivers, lakes, or oceans.
Can contain fossils from plants and animals.
Example: limestone, sandstone
🔥 Metamorphic Rocks
Metamorphic rocks are formed when existing rocks are changed by heat and pressure, without melting.
The rock’s structure and minerals rearrange, creating a new kind of rock.
Example: marble (from limestone), slate (from shale)
Rock Examples:
Type | Example | How It Forms |
Igneous | Basalt, granite | Cooling of lava or magma |
Sedimentary | Limestone, sandstone | Layers of sediment compacted and cemented |
Metamorphic | Marble, slate | Heat and pressure on existing rock |
Common Rock Cycle Terms
Term | Meaning |
Magma | Melted rock beneath Earth’s surface. |
Lava | Magma that reaches the surface. |
Sediments | Small rock or organic particles. |
Compaction | Pressing sediments together. |
Cementation | Gluing sediments into solid rock. |
Deposition | Sediments being dropped in a new place. |
Metamorphism | Changing rock by heat and pressure. |
🌍 Processes in the Rock Cycle
Process | Description |
Weathering | Rocks are broken down into smaller pieces by wind, water, ice, or temperature changes. |
Erosion | Movement of rock particles by wind, water, or ice. |
Deposition | Dropping off of sediments in a new place. |
Compaction & Cementation | Layers of sediment are pressed and stuck together to form sedimentary rocks. |
Melting | Rocks become magma under extreme heat. |
Cooling & Solidification | Magma or lava cools and hardens into igneous rock. |
Heat & Pressure (Metamorphism) | Existing rocks are altered to form metamorphic rocks. |
Metamorphism:
Changing rock by heat and pressure. Metamorphic rocks can form from any type of rock (not just other metamorphic rocks).
Weathering
Weathering is the breaking down of rocks into smaller pieces. It happens in place (the rock doesn’t move yet) and can be caused by:
🪨 The rock stays where it is — it's just broken down into smaller bits like sand or soil.
Types of Weathering
Biological Weathering 🌱
Caused by plants and animals.
Example: Roots growing in cracks, animals digging.
Chemical Weathering 🧪
Water or air reacts with minerals in the rock.
Example: Acid rain dissolving limestone.
Physical (Mechanical) Weathering 🧊
Rocks break from temperature changes, freeze-thaw, or abrasion.
Example: Water freezes in a crack, expands, and breaks the rock.
🌊 Erosion
Erosion is the movement of rock particles from one place to another.
It happens when weathered pieces of rock are carried away by:
Water (rivers, rain)
Wind
Ice (glaciers)
Gravity
🏞️ Erosion moves the broken pieces to a new location, where they can be dropped off — this is called deposition.
Top Tips
🔄 Think of the rock cycle like recycling—rocks are constantly changing form.
🌋 Igneous = lava or magma cooling into rock.
🏞️ Sedimentary = sediments squashed together over time.
🔥 Metamorphic = existing rocks changed by heat and pressure.
💦 Weathering breaks rocks down, erosion moves them, and deposition drops them off.
🌱 Biological weathering = roots and animals;
🧪 Chemical weathering = acid rain or reactions;
🧊 Physical weathering = freeze-thaw or waves.
🏞️ Erosion = moves the broken pieces to a new location