Learning Objectives

• Differentiate between the three main types of rocks: igneous, sedimentary, and metamorphic.

• Describe the rock cycle and the processes that transform one type of rock into another.

• Explain the formation and characteristics of intrusive and extrusive igneous rocks.

• Describe how heat and pressure alter existing rocks to form metamorphic rocks.

Key Vocabulary

Rock Cycle

The series of processes that create and change rocks in Earth's crust over long periods of time.

Igneous Rock

A type of rock formed when hot, molten magma or lava cools down and becomes solid.

Sedimentary Rock

Rock formed from sediments, which are then compacted and cemented together over a long period of time.

Metamorphic Rock

Rock that has changed from one form to another due to intense heat and immense pressure.

Magma

Hot, semi-fluid material found beneath the Earth's crust from which lava and igneous rocks are formed.

Lava

Hot molten rock that has erupted from a volcano or fissure onto the Earth’s surface.

Key Vocabulary

Weathering

The process where rock is worn away or broken down into much smaller pieces.

Erosion

The process where earthen materials are worn away and moved by forces like wind or water.

Foliation

The repetitive layering in metamorphic rocks, creating bands of different colored crystals from pressure.

Cementation

The process where dissolved minerals crystallize and glue sediment particles together into a single mass.

What Are Rocks and the Rock Cycle?

• Rocks are classified by how they form as igneous, sedimentary, or metamorphic.

• The rock cycle is the process of one rock type changing into another.

• Energy from the Sun and Earth's interior drives the rock cycle's changes.

• Earth’s systems like the geosphere and hydrosphere interact to transform these rocks.

Igneous Rocks: Formed from Fire

Intrusive Rocks

• Forms when magma gets trapped and cools slowly beneath Earth's surface.

• Slow cooling allows large mineral crystals to form, creating a coarse-grained texture.

• A common example of this type of rock is granite.

Extrusive Rocks

• Forms when lava erupts onto the surface and cools down very quickly.

• Rapid cooling results in very small crystals, leading to a fine-grained texture.

• Examples include basalt, pumice, and obsidian, which can have a glassy texture.

Sedimentary Rocks: A Story in Layers

Formation Process

• Weathering breaks down rocks into small pieces, and erosion carries them away.

• These pieces, called sediments, are deposited and settle into many different layers.

• Compaction and cementation press and glue these layers together into solid rock.

Other Formation Types

• Chemical rocks form when minerals that are dissolved in water crystallize.

• Organic rocks are made from the built-up remains of once-living things.

• Limestone is an organic rock, while rock salt is a chemical rock.

Metamorphic Rocks: Changed by Heat and Pressure

• Existing rocks are changed by intense heat and pressure deep within the Earth.

• Extreme pressure can create parallel bands or layers, a feature called foliation.

• For example, shale turns into slate, and limestone changes into marble.

Common Misconceptions

Summary

• The three main rock types are igneous, sedimentary, and metamorphic.

• The rock cycle illustrates the continuous transformation of rocks over time.

• Igneous, sedimentary, and metamorphic rocks have unique formation processes.

• Rocks provide important clues about Earth’s geological history.