The Rock Cycle
Learn how rocks transform into different types through melting, cooling, weathering, erosion, deposition, compaction, and heat and pressure in the rock cycle.
What you'll do in this lesson
A voice-first session with the Crimsora tutor on The Rock Cycle, then targeted practice and FRQs — with the tutor adapting to where you get stuck.
What this lesson covers
Rocks are not permanent. Over millions of years, a granite mountain can become sandstone, which can become slate, which can become magma, which can cool into new granite. This transformation cycle—the rock cycle—has no beginning and no end. In this lesson, you'll trace pathways through the rock cycle and learn to predict how different processes can turn any rock type into any other. Understanding the rock cycle helps explain how Earth's crust constantly recycles itself and why different rock types appear in different locations.
What Is the Rock Cycle?
The rock cycle is the continuous process by which rocks form, break down, and reform over geological time. Unlike a simple cycle with a fixed order, the rock cycle can move in any direction. A rock can follow many different pathways depending on which processes act on it and where it ends up on Earth.
Three main rock types exist—igneous, sedimentary, and metamorphic—and the rock cycle shows how one type can transform into another. For example, igneous rock at Earth's surface can weather into sand grains, which get transported by rivers, deposited in layers, and then compacted and cemented into sedimentary rock. That sedimentary rock can later be buried deep underground where heat and pressure transform it into metamorphic rock. If that metamorphic rock is pushed even deeper and heated until it melts, it becomes magma, which eventually cools to form new igneous rock. The cycle then continues.
The rock cycle never stops because Earth's internal heat, weathering processes, and plate tectonics constantly move rocks through different conditions. Understanding the rock cycle explains why you might find marine fossils in sandstone on a mountaintop—that rock was once on an ocean floor—and why different areas have different rock types.
Three main rock types exist—igneous, sedimentary, and metamorphic—and the rock cycle shows how one type can transform into another. For example, igneous rock at Earth's surface can weather into sand grains, which get transported by rivers, deposited in layers, and then compacted and cemented into sedimentary rock. That sedimentary rock can later be buried deep underground where heat and pressure transform it into metamorphic rock. If that metamorphic rock is pushed even deeper and heated until it melts, it becomes magma, which eventually cools to form new igneous rock. The cycle then continues.
The rock cycle never stops because Earth's internal heat, weathering processes, and plate tectonics constantly move rocks through different conditions. Understanding the rock cycle explains why you might find marine fossils in sandstone on a mountaintop—that rock was once on an ocean floor—and why different areas have different rock types.
The Seven Key Processes in the Rock Cycle
Seven main processes drive rock transformations. Melting occurs when rock is heated to extremely high temperatures deep underground or near magma, turning solid rock into molten material. Cooling is the opposite: when magma rises toward the surface or cools underground, it solidifies into igneous rock.
Weathering breaks rock into smaller pieces through physical forces (like freezing and thawing) or chemical breakdown (like water dissolving minerals). Erosion removes and transports weathered rock material by wind, water, or ice. Deposition drops that sediment in new locations, such as river valleys or ocean floors, where it accumulates in layers.
Compaction and cementation bind loose sediment grains together under the weight of overlying layers (compaction) and by minerals crystallizing between grains (cementation), forming sedimentary rock. Heat and pressure deep underground change the mineral structure and texture of any rock type without melting it completely, creating metamorphic rock.
Each process links to the next in the cycle. Weathering always precedes erosion, and erosion always precedes deposition. Deposition always comes before compaction and cementation. However, the entry point into this sequence varies: some rocks enter through melting and cooling, others through weathering, and others through heat and pressure.
Weathering breaks rock into smaller pieces through physical forces (like freezing and thawing) or chemical breakdown (like water dissolving minerals). Erosion removes and transports weathered rock material by wind, water, or ice. Deposition drops that sediment in new locations, such as river valleys or ocean floors, where it accumulates in layers.
Compaction and cementation bind loose sediment grains together under the weight of overlying layers (compaction) and by minerals crystallizing between grains (cementation), forming sedimentary rock. Heat and pressure deep underground change the mineral structure and texture of any rock type without melting it completely, creating metamorphic rock.
Each process links to the next in the cycle. Weathering always precedes erosion, and erosion always precedes deposition. Deposition always comes before compaction and cementation. However, the entry point into this sequence varies: some rocks enter through melting and cooling, others through weathering, and others through heat and pressure.
Tracing Rock-Cycle Pathways
To predict which processes could transform one rock type into another, identify the starting rock type and the target rock type, then choose a logical sequence of processes that connects them.
Consider this example: How can granite (igneous) become sandstone (sedimentary)? The pathway is: weathering → erosion → deposition → compaction and cementation. Granite at the surface breaks apart through weathering, fragments are carried away by erosion, they settle into layers through deposition, and finally they are pressed and cemented together into sandstone.
Now consider: How can sandstone (sedimentary) become slate (metamorphic)? The pathway is: heat and pressure. If sandstone is buried deep underground in a region with tectonic activity, intense heat and pressure transform it into slate without melting.
Or: How can slate (metamorphic) become granite (igneous)? The pathway is: melting → cooling. If slate is pushed even deeper toward magma or encounters extreme heat, it melts into magma. When that magma eventually cools, it crystallizes into granite.
The key insight is that the rock cycle has no fixed order and no required sequence. Any rock type can reach any other rock type if the right conditions occur. The specific pathway depends on Earth's processes and where the rock is located in the cycle at any given time.
Consider this example: How can granite (igneous) become sandstone (sedimentary)? The pathway is: weathering → erosion → deposition → compaction and cementation. Granite at the surface breaks apart through weathering, fragments are carried away by erosion, they settle into layers through deposition, and finally they are pressed and cemented together into sandstone.
Now consider: How can sandstone (sedimentary) become slate (metamorphic)? The pathway is: heat and pressure. If sandstone is buried deep underground in a region with tectonic activity, intense heat and pressure transform it into slate without melting.
Or: How can slate (metamorphic) become granite (igneous)? The pathway is: melting → cooling. If slate is pushed even deeper toward magma or encounters extreme heat, it melts into magma. When that magma eventually cools, it crystallizes into granite.
The key insight is that the rock cycle has no fixed order and no required sequence. Any rock type can reach any other rock type if the right conditions occur. The specific pathway depends on Earth's processes and where the rock is located in the cycle at any given time.
Common Starting Points and Transformations
Understanding where rocks commonly enter the cycle helps predict realistic pathways. Igneous rocks typically start the cycle when magma cools. From there, igneous rocks can weather into sediment, be buried and compressed into sedimentary rock, or be subjected to heat and pressure to become metamorphic rock, or melt again if pushed deeper.
Sedimentary rocks begin their journey when sediment is deposited and cemented. From there, they can be uplifted and weathered back into sediment, buried and heated to become metamorphic rock, or melted if pushed toward magma.
Metamorphic rocks form when any rock type is buried and exposed to heat and pressure. From there, they can be uplifted and weathered into sediment, melted into magma, or remain stable if conditions do not change.
Many students think the rock cycle always moves in one direction (igneous → sedimentary → metamorphic → igneous), but this is incorrect. A metamorphic rock can be uplifted and weathered directly into sediment without ever being igneous. A sedimentary rock can melt into magma without first becoming metamorphic. The rock cycle truly allows multiple pathways, and recognizing this flexibility is essential for understanding how Earth's crust recycles itself over time.
Sedimentary rocks begin their journey when sediment is deposited and cemented. From there, they can be uplifted and weathered back into sediment, buried and heated to become metamorphic rock, or melted if pushed toward magma.
Metamorphic rocks form when any rock type is buried and exposed to heat and pressure. From there, they can be uplifted and weathered into sediment, melted into magma, or remain stable if conditions do not change.
Many students think the rock cycle always moves in one direction (igneous → sedimentary → metamorphic → igneous), but this is incorrect. A metamorphic rock can be uplifted and weathered directly into sediment without ever being igneous. A sedimentary rock can melt into magma without first becoming metamorphic. The rock cycle truly allows multiple pathways, and recognizing this flexibility is essential for understanding how Earth's crust recycles itself over time.
Why the Rock Cycle Matters
The rock cycle explains why rocks are not permanent features of Earth. It connects the processes you observe at the surface—like erosion and weathering—to deeper geological events like mountain formation and magma activity. Over hundreds of millions of years, the rock cycle reshapes continents, creates new crust, and recycles old crust back into the mantle.
The rock cycle also explains practical observations. Why do mountains eventually wear down? Weathering and erosion. Why do sedimentary rocks with fossils appear on mountaintops? Because they formed as sediment on an ancient seafloor and were later uplifted. Why do different regions have different rock types? Because each area has experienced different parts of the rock cycle at different times.
In your own community, you are walking on rocks that have gone through multiple rock-cycle transformations. Understanding the rock cycle lets you read Earth's history in the rocks beneath your feet.
The rock cycle also explains practical observations. Why do mountains eventually wear down? Weathering and erosion. Why do sedimentary rocks with fossils appear on mountaintops? Because they formed as sediment on an ancient seafloor and were later uplifted. Why do different regions have different rock types? Because each area has experienced different parts of the rock cycle at different times.
In your own community, you are walking on rocks that have gone through multiple rock-cycle transformations. Understanding the rock cycle lets you read Earth's history in the rocks beneath your feet.
Key terms
- Rock cycle.
- The continuous process by which rocks form, break down, and transform into different types through melting, cooling, weathering, erosion, deposition, compaction, cementation, and heat and pressure.
- Melting.
- The process by which solid rock is heated to extremely high temperatures and turns into molten magma.
- Cooling.
- The process by which magma or molten rock loses heat and solidifies into solid igneous rock.
- Weathering.
- The breakdown of rock into smaller pieces through physical forces or chemical reactions at or near Earth's surface.
- Erosion.
- The removal and transport of rock material and sediment by water, wind, ice, or gravity.
- Deposition.
- The process by which sediment that has been transported by erosion settles and accumulates in a new location.
- Compaction and cementation.
- Two related processes where sediment is pressed together by weight (compaction) and minerals crystallize between grains (cementation) to form solid sedimentary rock.
- Heat and pressure.
- Conditions deep underground that change the mineral structure and texture of rock, forming metamorphic rock without melting.
Worked example
A student finds a piece of marble (metamorphic rock) in a field. The marble sits at Earth's surface where it experiences weathering. Describe the sequence of rock-cycle processes that could turn this marble into granite (igneous rock), and explain why each process must occur in the order you list.
To transform marble (metamorphic) into granite (igneous), we need to melt the rock and then cool it. Here is the complete pathway:
Step 1: Weathering and erosion. The marble at the surface breaks apart through weathering—perhaps frozen water expands in cracks, or minerals dissolve in rainwater. Erosion then carries the broken marble fragments away as sediment.
Step 2: Deposition. The sediment settles into layers in a location like a riverbed or ocean floor. It accumulates in thick layers over time.
Step 3: Compaction and cementation. The weight of overlying sediment compacts the marble fragments together. Minerals crystallize between grains, cementing them into solid rock.
Step 4: Melting. This newly cemented rock is eventually buried very deep underground by tectonic forces, or it moves close to a magma chamber where it is heated to extremely high temperatures. It melts into magma.
Step 5: Cooling. As the magma rises toward the surface or as the region cools, the magma solidifies slowly into granite (igneous rock).
Why this order? Melting cannot happen until the marble is first broken down into sediment and then reassembled—you cannot jump directly from solid marble to magma. Cooling must come last because magma must exist before it can cool. Deposition must precede compaction and cementation because grains must be present and settled before they can be pressed together. Each step creates the conditions for the next.
Note: Another valid pathway would be melting first (if the marble encounters extreme heat deep underground) and then cooling directly into granite, without passing through the sedimentary stage. The rock cycle allows multiple pathways.
Step 1: Weathering and erosion. The marble at the surface breaks apart through weathering—perhaps frozen water expands in cracks, or minerals dissolve in rainwater. Erosion then carries the broken marble fragments away as sediment.
Step 2: Deposition. The sediment settles into layers in a location like a riverbed or ocean floor. It accumulates in thick layers over time.
Step 3: Compaction and cementation. The weight of overlying sediment compacts the marble fragments together. Minerals crystallize between grains, cementing them into solid rock.
Step 4: Melting. This newly cemented rock is eventually buried very deep underground by tectonic forces, or it moves close to a magma chamber where it is heated to extremely high temperatures. It melts into magma.
Step 5: Cooling. As the magma rises toward the surface or as the region cools, the magma solidifies slowly into granite (igneous rock).
Why this order? Melting cannot happen until the marble is first broken down into sediment and then reassembled—you cannot jump directly from solid marble to magma. Cooling must come last because magma must exist before it can cool. Deposition must precede compaction and cementation because grains must be present and settled before they can be pressed together. Each step creates the conditions for the next.
Note: Another valid pathway would be melting first (if the marble encounters extreme heat deep underground) and then cooling directly into granite, without passing through the sedimentary stage. The rock cycle allows multiple pathways.
Practice questions
A piece of limestone (sedimentary rock) is carried deep underground by plate tectonics and subjected to intense heat and pressure, but it does not melt. What rock type will it become, and which process causes this transformation?
Answer: It will become metamorphic rock, caused by heat and pressure.
When any rock is heated and pressured underground without melting completely, its minerals recrystallize and its structure changes, forming metamorphic rock. This is different from melting, which would turn the rock into magma. The key clue is 'does not melt'—that tells you heat and pressure, not melting, is the process at work.
Which of the following sequences correctly describes one possible pathway through the rock cycle?
- Melting → cooling → heat and pressure → metamorphic rock
- Deposition → weathering → erosion → sediment
- Weathering → erosion → deposition → compaction and cementation
- Heat and pressure → melting → cooling → limestone
Answer: Weathering → erosion → deposition → compaction and cementation
This sequence follows the correct order of processes that form sedimentary rock from weathered material. Weathering breaks down rock, erosion transports the pieces, deposition drops them in layers, and compaction and cementation bind them into rock. The first choice is wrong because heat and pressure come before melting, not after cooling. The second choice reverses the correct order—weathering must come before erosion. The fourth choice is illogical because heat and pressure do not precede melting (melting is the result of extreme heat).
Explain how a piece of granite at the surface could eventually become sedimentary rock. In your explanation, identify at least three processes that must occur and describe what happens at each step.
Answer: Weathering breaks the granite into sand and smaller pieces. Erosion carries these pieces away by water or wind. Deposition drops the sediment into layers, where compaction and cementation press the grains together and bind them with minerals, forming sedimentary rock.
A complete answer names and describes at least three processes in order. Weathering must come first because solid rock must break apart before it can be transported. Erosion must come second because sediment must be moved to a new location. Deposition must follow erosion because sediment must settle before it can be cemented. Compaction and cementation complete the formation of sedimentary rock. A common mistake is reversing the order or leaving out erosion, which is essential for moving the weathered material to a new location.
FAQ
- Does the rock cycle always follow the same path, or can rocks take different routes?
- Rocks can take many different routes through the rock cycle. A sedimentary rock does not have to become metamorphic before becoming igneous—it can melt directly into magma under the right conditions. A metamorphic rock does not have to follow any fixed sequence. The specific pathway depends on where the rock is located and which geological processes affect it. This is why the rock cycle is drawn as a circle with multiple arrows pointing in different directions, not a simple one-way path.
- Can a rock type change into another rock type without going through weathering?
- Yes. For example, sandstone (sedimentary) can be buried and heated to become slate (metamorphic) through heat and pressure alone, without weathering. Or metamorphic rock can melt into magma and cool into igneous rock without any weathering involved. Weathering is only necessary if rock material is going to be broken apart and transported to form new sedimentary rock.
- How long does the rock cycle take?
- The rock cycle takes millions of years. A single rock might spend millions of years in one location before conditions change and it begins to transform. For example, a mountain of granite might take 50 to 100 million years to weather away, be transported, and become sedimentary rock. These timescales are so long that we cannot observe the complete cycle in a human lifetime, which is why geologists study rock layers and use dating methods to understand these processes.
- Why do we need to know about the rock cycle if rocks seem permanent?
- Rocks seem permanent because human lifetimes are incredibly short compared to geological time. The rock cycle shows that Earth's surface is constantly changing—mountains erode, new rock forms, and continents move. Understanding the rock cycle helps explain why different rocks appear in different places, why we find fossils in rocks, why mountains have layers, and how Earth recycles its own materials. It is fundamental to understanding Earth's structure and how it works.
Learn this with a teacher, not a page
The Crimsora tutor teaches The Rock Cycle live — explaining on a whiteboard, asking you questions, and adapting to where you get stuck.