The rock cycle and Earth's materials

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Lesson notes

The Three Main Rock Types

**Igneous rocks** form when magma or lava cools and solidifies.
**Sedimentary rocks** form from compaction and cementation of sediments (fragments, minerals, or organic matter).
**Metamorphic rocks** form when existing rocks are changed by heat, pressure, or chemical fluids.
Each rock type can be transformed into another through the **rock cycle**.

Formation of Igneous Rocks

Magma that cools slowly **inside Earth** forms **intrusive (plutonic)** rocks like granite, with coarse grains.
Lava that cools quickly **on Earth's surface** forms **extrusive (volcanic)** rocks like basalt, with fine grains.
Very rapid cooling can produce natural glass, such as **obsidian**.
Any rock type can melt into magma and later cool into igneous rock.

Formation of Sedimentary Rocks

**Weathering and erosion** break rocks into smaller fragments (sediments).
Sediments are transported by water, wind, or ice and deposited in layers.
**Lithification** (compaction and cementation) turns sediments into sedimentary rock.
Types include **clastic** (from rock fragments), **biogenic** (from organisms, e.g., fossils), and **precipitate** (from evaporated solutions).

Formation of Metamorphic Rocks

**Regional metamorphism** occurs over large areas due to mountain-building, often producing **foliated** rocks with bands.
**Contact metamorphism** happens when magma heats surrounding rock, causing recrystallization.
Metamorphism can change the mineral composition and texture without melting the rock.
Any pre-existing rock type can undergo metamorphism.

Driving Forces of the Rock Cycle

**Plate tectonics** drives the rock cycle by moving rocks between surface and deep Earth.
The **water cycle** contributes through weathering, erosion, and transport of sediments.
**Heat from Earth's interior** and **solar energy** power the processes of melting, metamorphism, and weathering.
The **Wilson cycle** describes how ocean basins open and close, recycling rocks over geologic time.

Key Processes in the Rock Cycle

**Melting** transforms solid rock into magma.
**Cooling and crystallization** form igneous rocks from magma/lava.
**Weathering and erosion** break down rocks into sediments.
**Lithification** compacts and cements sediments into sedimentary rocks.
**Metamorphism** alters rocks under heat and pressure.

The rock cycle showing transitions between igneous, sedimentary, and metamorphic rocks, with magma as the source of igneous rocks.

Comparison of rock formation settings: intrusive vs. extrusive igneous, sedimentary, and metamorphic.

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Practice questions

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1.Which of the following is NOT one of the three main rock types?
Easy
- AIgneous
- BSedimentary
- CMetamorphic
- DMagmatic
2.What process transforms sedimentary rock into metamorphic rock?
Easy
- AWeathering and erosion
- BMelting and cooling
- CHeat and pressure
- DCompaction and cementation
3.Which type of rock forms from the cooling and solidification of magma?
Easy
- ASedimentary
- BMetamorphic
- CIgneous
- DClastic
4.What type of rock is formed from the lithification of sediment?
Easy
- AIgneous
- BMetamorphic
- CSedimentary
- DVolcanic
5.Which of the following processes is part of the rock cycle?
Medium
- APhotosynthesis
- BEvaporation
- CMetamorphism
- DCondensation
6.What is the main driving force behind the rock cycle?
Medium
- AWind and water
- BPlate tectonics
- CSolar radiation
- DGravity
7.Which rock type is formed when magma cools slowly beneath the Earth's surface?
Medium
- AExtrusive igneous
- BIntrusive igneous
- CClastic sedimentary
- DFoliated metamorphic
8.What type of metamorphism is caused by contact with a hot magma body?
Medium
- ARegional metamorphism
- BContact metamorphism
- CDynamic metamorphism
- DShock metamorphism

Revision notes

## The Rock Cycle & Earth's Materials The rock cycle describes how Earth's three main rock types—**igneous**, **sedimentary**, and **metamorphic**—transform into one another over geologic time. The cycle is driven by **plate tectonics** and the **water cycle**, which provide the energy and forces needed to change rocks. ### Key Processes - **Weathering & Erosion**: Rocks at the surface break down (weathering) and are transported (erosion) by wind, water, or ice. - **Lithification**: Sediments are buried, compacted, and cemented to form **sedimentary rocks**. - **Metamorphism**: Heat and pressure (from burial or nearby magma) change rocks physically or chemically into **metamorphic rocks**. - **Melting & Crystallization**: Rocks deep underground melt into magma. When magma cools, it solidifies into **igneous rocks**. ### Rock Types & Formation | Rock Type | How It Forms | Examples | |-----------|--------------|----------| | **Igneous** | Cooling of magma/lava | Granite (intrusive, coarse-grained), Basalt (extrusive, fine-grained), Obsidian (glass) | | **Sedimentary** | Lithification of sediments (clastic, biogenic, or chemical) | Sandstone (clastic), Limestone (biogenic), Rock salt (chemical) | | **Metamorphic** | Heat/pressure altering existing rocks | Slate (from shale), Marble (from limestone), Gneiss (banded) | ### Driving Forces - **Plate Tectonics**: The Wilson cycle (opening/closing of ocean basins) drives subduction, mountain building, and volcanism, which power the rock cycle. - **Water Cycle**: Water aids weathering, erosion, and transport of sediments. ### Important Definitions - **Magma**: Molten rock beneath Earth's surface. - **Lava**: Magma that reaches the surface. - **Foliation**: Banding in metamorphic rocks due to pressure. - **Contact Metamorphism**: Heat from nearby magma alters surrounding rock. - **Regional Metamorphism**: Large-scale metamorphism during mountain building. ### Quick Tips - Any rock type can become any other rock type through the right processes. - The rock cycle is a **biogeochemical cycle** on Earth (involves life, geology, and chemistry).

Rock cycle: The continuous process by which rocks change from one type to another over geologic time, driven by plate tectonics and the water cycle.
Igneous rock: Rock formed from the cooling and crystallization of magma or lava.
Sedimentary rock: Rock formed from the lithification of sediments (fragments, organic material, or chemical precipitates).
Metamorphic rock: Rock formed when existing rocks are changed by heat, pressure, or chemically active fluids.
Weathering: The breakdown of rocks at Earth's surface by physical, chemical, or biological processes.
Erosion: The transport of weathered rock fragments by natural agents like water, wind, or ice.
Lithification: The process of compacting and cementing sediments into solid rock.
Metamorphism: The alteration of rocks by heat, pressure, or chemical fluids, resulting in new minerals or textures.
Magma: Molten rock beneath Earth's surface.
Lava: Magma that has reached Earth's surface.
Foliation: A banded or layered appearance in metamorphic rocks caused by pressure.
Plate tectonics: The theory that Earth's lithosphere is divided into plates that move, driving processes like mountain building and volcanism.
Wilson cycle: The cycle of opening and closing of ocean basins due to plate tectonics.

Flashcards

What are the three main types of rocks in the rock cycle?

Igneous, sedimentary, and metamorphic.

What processes transform rocks into sedimentary rocks?

Weathering and erosion break rocks into fragments, which are then transported, deposited, compacted, and lithified.

What is lithification?

The process of compacting and cementing sediments into solid sedimentary rock.

Name the three types of sedimentary rocks based on formation.

Clastic (fragments), biogenic (organic material), and precipitate (chemical evaporation).

What is metamorphism?

The process by which rocks are changed physically or chemically by high temperatures and pressures to form metamorphic rocks.

What is the difference between regional and contact metamorphism?

Regional metamorphism affects large areas due to mountain building; contact metamorphism occurs when rock is heated by nearby magma.

What is foliation in metamorphic rocks?

Bands of differing mineralogy and color caused by regional metamorphism.

How do igneous rocks form?

When magma cools and crystallizes, either underground (intrusive) or on the surface (extrusive).

What is the difference between intrusive and extrusive igneous rocks?

Intrusive rocks cool slowly underground, forming coarse-grained textures (e.g., granite); extrusive rocks cool rapidly on the surface, forming fine-grained textures (e.g., basalt).

What is obsidian?

A natural glass formed when lava cools so rapidly that no crystals form.

Can any rock type become magma?

Yes, any of the three main rock types can melt into magma under high temperatures and pressures.

What drives the rock cycle?

Plate tectonics and the water cycle provide the energy and forces that drive the rock cycle.

What is the Wilson cycle?

The repeated opening and closing of ocean basins due to plate tectonics, which drives the rock cycle.

What is weathering?

The breakdown of rocks at Earth's surface by physical or chemical processes.

What is erosion?

The transport of weathered rock fragments by natural agents like water, wind, or ice.

What is compaction in sedimentary rock formation?

The process where buried sediment layers are pressed together by overlying material.

What is metasomatism?

The addition of chemicals from magma to surrounding rock during contact metamorphism.

What is a clastic sedimentary rock?

A rock formed from fragments (clasts) of other rocks, such as sandstone or shale.

What is a biogenic sedimentary rock?

A rock formed from the remains of living organisms, like limestone from shells.

What is a precipitate sedimentary rock?

A rock formed when minerals crystallize from evaporating water, like rock salt.

What is the rock cycle?

The continuous process by which rocks change from one type to another over geologic time.

What is the role of subduction in the rock cycle?

Subduction carries rocks deep into Earth, where they may melt into magma or undergo metamorphism.

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