Rocks and the Rock Cycle
Grade 5 · Science · Study Guide
Discover how rocks form, change, and recycle through Earth's three rock types over millions of years.
Rocks are constantly being made, broken down, and remade — just very, very slowly. The rock cycle describes how rocks change from one type to another through natural processes driven by heat, pressure, weathering, and melting. There are three main types of rock: igneous, sedimentary, and metamorphic, and every rock on Earth has traveled through this cycle.
Igneous rocks form when molten rock (magma) cools and hardens. When magma erupts from a volcano it is called lava, and it cools quickly on Earth's surface to form fine-grained rocks like basalt. Magma that cools slowly deep underground forms coarse-grained rocks like granite, because slow cooling gives crystals time to grow large. About 90% of Earth's crust is made of igneous rock.
Sedimentary rocks form from sediment — tiny particles of sand, silt, clay, shells, or other material — that accumulates in layers and is compressed over time. The layers (strata) are like pages in a history book; deeper layers are generally older. Fossils are almost exclusively found in sedimentary rock because soft tissues and bones can be preserved as sediment buries organisms. Limestone, sandstone, and shale are common sedimentary rocks.
Metamorphic rocks form when existing rocks are changed by intense heat and pressure deep in Earth's crust — without actually melting. The minerals recrystallize into new arrangements, creating banded or foliated patterns. Marble is metamorphic limestone; slate is metamorphic shale; quartzite is metamorphic sandstone. If metamorphic rock gets hot enough, it melts and becomes magma, starting the cycle again.
| Rock Type | How It Forms | Common Example | Notable Feature |
|---|---|---|---|
| Igneous | Magma/lava cools and hardens | Granite, Basalt | May have crystals or bubbles |
| Sedimentary | Sediment compacts in layers | Sandstone, Limestone | Has visible layers; may contain fossils |
| Metamorphic | Heat and pressure transform rock | Marble, Slate | Banded or foliated texture |
Key terms
- Igneous rock
- Rock formed when magma or lava cools and solidifies.
- Sedimentary rock
- Rock formed from layers of sediment that are compacted and cemented together over time.
- Metamorphic rock
- Rock changed by heat and pressure (without melting) into a new form.
- Magma
- Molten rock found beneath Earth's surface.
- Lava
- Magma that reaches Earth's surface, usually through a volcano.
- Sediment
- Tiny particles of rock, sand, silt, and organic material that settle in layers.
- Rock cycle
- The continuous process by which rocks change from one type to another over millions of years.
Flashcards
- Igneous rock
- Rock formed from cooled magma or lava; examples include granite and basalt.
- Sedimentary rock
- Rock formed from layered, compressed sediment; examples include sandstone and limestone.
- Metamorphic rock
- Rock changed by heat and pressure; examples include marble and slate.
- Magma
- Molten rock beneath Earth's surface.
- Rock cycle
- The continuous process by which rocks change between igneous, sedimentary, and metamorphic types.
- Stratum (strata)
- A layer of sedimentary rock; deeper strata are generally older.
Practice questions
Which type of rock forms when magma cools and hardens?
- Sedimentary
- Metamorphic
- Igneous
- Mineral
Show answer
Answer: Igneous
Igneous comes from the Latin word for fire. These rocks are literally born from fire — the cooling of molten magma or lava.
Fossils are most commonly found in metamorphic rocks.
Show answer
Answer: False
Fossils form in sedimentary rock, where organisms get buried in sediment before it hardens. The intense heat and pressure that creates metamorphic rock destroys most fossils.
Marble is a ___ rock formed when limestone is changed by heat and pressure.
Show answer
Answer: metamorphic
Marble forms when limestone (sedimentary) is subjected to heat and pressure deep in Earth's crust, causing the calcite crystals to recrystallize.
What forms when sediment is compacted and cemented in layers over time?
- Igneous rock
- Lava
- Sedimentary rock
- Magma
Show answer
Answer: Sedimentary rock
Sedimentary rocks form through the process of deposition (sediment settles), compaction (weight squeezes sediment), and cementation (minerals glue particles together).
The rock cycle means rocks can change from one type to another over time.
Show answer
Answer: True
The rock cycle shows that no rock type is permanent — given enough time and the right conditions, any rock can become any other type.
Fun facts
- The granite countertops in many kitchens formed from magma that cooled slowly underground millions of years ago — your breakfast sits on ancient igneous rock.
- The White Cliffs of Dover in England are made of chalk, a type of sedimentary limestone built from the shells of microscopic sea creatures that lived 65-100 million years ago.
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