Rocks

3.1 The Rock Cycle

Rocks are any solid mass of minerals, or mineral-like matter, occurring naturally as part of our planet.

Types of Rocks

1. Igneous rock is formed by the crystallization (hardening) of molten magma.

Rocks

3.1 The Rock Cycle

Types of Rocks2. Sedimentary rock is formed from the

weathered products of preexisting rocks that have been transported, deposited, compacted, and cemented.

3. Metamorphic rock is formed by the alteration (change) of preexisting rock deep within Earth (but still in a solid state) by heat, pressure, and/or chemically active fluids.

The Rock Cycle

3.1 The Rock Cycle

Shows the relationships between the three rock types (igneous, sedimentary, metamorphic)

Magma is molten (melted) material that forms deep beneath the Earth’s surface.

Lava is magma that reaches the surface. Weathering is a process in which rocks are

broken down by water, air, and living things. Sediment is weathered pieces of Earth

elements.

3.1 The Rock Cycle

The Rock Cycle

3.1 The Rock Cycle

Magma forms when rock melts deep beneath Earth’s surface.

When magma or lava cools and hardens, igneous rocks form.

Rocks at Earth’s surface are broken down into smaller pieces called sediments.

When sediments are compacted and cemented, sedimentary rocks form.

Any type of rock that is changed by heat, pressure or chemicals becomes metamorphic.

Energy That Drives the Rock Cycle

3.1 The Rock Cycle

Processes driven by heat from the Earth’s interior are responsible for forming both igneous rock and metamorphic rock.

External processes produce sedimentary rocks.

Weathering and the movement of weathered materials are external processes powered by energy from the sun.

REVIEW

*Remember igneous rocks form when magma or lava cools and hardens. Different kinds of igneous rocks form when magma and lava cool and harden.

Formation of Igneous Rocks

3.2 Igneous Rocks

1. Intrusive igneous rocks are formed when magma hardens beneath Earth’s surface.

2. Extrusive igneous rocks are formed when lava hardens above Earth’s surface.

Classification of Igneous Rocks

3.2 Igneous Rocks

1. Texture

Igneous rocks can be classified based on their composition and texture.

• Coarse-grained texture is caused by slow cooling resulting in larger crystals.

• Fine-grained texture is caused by rapid cooling resulting in smaller, connected mineral grains.

Coarse-Grained Igneous Texture

Granite is an intrusive igneous rock that forms when magma cools slowly beneath Earth’s surface.

Fine-Grained Igneous Texture

Rhyolite is an extrusive igneous rock that forms when lava cools quickly at Earth’s surface.

Classification of Igneous Rocks

3.2 Igneous Rocks

1. Texture (continued)• Glassy texture is caused by very rapid cooling. • Porphyritic texture is caused by different rates of

cooling resulting in varied sized minerals.

2. Composition• Granitic composition rocks are made mostly

of light-colored quartz and feldspar.

Obsidian Exhibits a Glassy Texture.

Obsidian is an extrusive igneous rock.

Porphyritic Igneous Texture

Andesite displays igneous rock with a porphyritic texture. How did this rock probably form?

Classification of Igneous Rocks

3.2 Igneous Rocks

2. Composition (continued)• Basaltic composition rocks are made mostly of

dark-colored silicate minerals and feldspar.

• Andesitic composition rocks are between granitic light-color minerals and basaltic composition dark-colored minerals.

• Ultramafic composition rocks are made mostly from iron and magnesium-rich minerals.

Basalt

Basalt is an igneous rock made mostly of dark colored silicate minerals.

Classification of Igneous Rocks

REVIEW

Igneous rocks are classified based on their texture and composition.

Formation of Sedimentary Rocks

3.3 Sedimentary Rocks

• Erosion involves the weathering and the removal of rock.

• Deposition occurs when an agent of erosion—water, wind, ice, or gravity—loses energy and drops sediments.

Weathering, Erosion, and Deposition

Formation of Sedimentary Rocks

3.3 Sedimentary Rocks

• Compaction is a process that squeezes, or compacts, sediments.

• Cementation takes place when dissolved minerals are deposited in the tiny spaces among the sediments.

Compaction and Cementation

Classification of Sedimentary Rocks

3.3 Sedimentary Rocks

1. Clastic sedimentary rocks are composed of weathered bits of rocks and minerals.

• Classified by particle size

Two Main Groups

- Shale (most abundant)• Common rocks include

- Conglomerate

- Sandstone

Shale with Plant Fossils

Conglomerate

Conglomerate is made of rounded pebbles cemented together.

Classification of Sedimentary Rocks

3.3 Sedimentary Rocks

Two Main Groups2. Chemical sedimentary rocks form when

dissolved substances precipitate, or separate, from water. • Common rocks include

- limestone—most abundant chemical rock

- microcrystalline quartz known as chert, flint, jasper, or agate

- evaporites such as rock salt or gypsum - coal

Fossiliferous Limestone

This biochemical rock, called coquina, is a type of limestone that is made of hundreds of shell fragments.

Classification of Sedimentary Rocks

Features of Some Sedimentary Rocks

3.3 Sedimentary Rocks

Features of sedimentary rocks are clues to how and where the rocks are formed

In undisturbed rocks, the oldest layers are found at the bottom.

Ripple marks indicate that the rock may have formed along a beach or stream.

Mud cracks can indicate the rock formed in a dry environment.

Formation of Metamorphic Rocks

3.4 Metamorphic Rocks

Metamorphism means “to change form.”

Conditions for formation are found a few kilometers below the Earth’s surface and extend into the upper mantle.

Most metamorphic changes occur at elevated temperatures and pressures.

Formation of Metamorphic Rocks

3.4 Metamorphic Rocks

Contact metamorphism occurs when magma moves into rock.

• Changes are driven by a rise in temperature.

• Occurs near a body of magma

Formation of Metamorphic Rocks

3.4 Metamorphic Rocks

Regional metamorphism results in large-scale deformation and high-grade metamorphism. • Directed pressures and high temperatures

occur during mountain building.

• Produces the greatest volume of metamorphic rock

Agents of Metamorphism

3.4 Metamorphic Rocks

Heat

Pressure

• Provides the energy needed to drive chemical reactions

• Causes a more compact rock with greater density

Agents of Metamorphism

3.4 Metamorphic Rocks

• Hot water-based solutions escaping from the mass of magma

• Promote recrystallization by dissolving original minerals and then depositing new ones

Hydrothermal Solutions

Classification of Metamorphic Rocks

3.4 Metamorphic Rocks

1. Foliated Metamorphic Rock

2. Nonfoliated Metamorphic Rock

Two main categories

• Has a banded or layered appearance

• Does not have a banded texture

Classification of Metamorphic Rocks

Gneiss Typically Displays a Banded Appearance

Marble—A Nonfoliated Metamorphic Rock