Introduction to the Rock Cycle

Intro to the Rock Cycle

Today's Objectives

• What is a rock?

• What are the 3 main types of rocks?

• What is the rock cycle?

Open Ended

Look at the picture of the 3 types of rocks. What is one similarity OR one difference between the rocks?

Minerals and Rocks

• Mineral: a solid that is formed naturally in the earth and normally has a crystal structure

• Rock: a solid that is made up of one or more minerals

• Minerals are the "building blocks" of rocks.

Types of Rocks

• Rocks are classified into 3 categories, based on how they are formed

• Does anyone know what the three categories are?

• Answer: igneous, metamorphic, and sedimentary

Multiple Choice

How many categories of rocks are there?

• 1

• 2

• 3

• 4

1. Igneous Rocks

• Igneous rocks are formed by magma/lava.

• When a volcano erupts, it spews out hot molten rock called lava. Eventually the lava will cool down and become solid. This forms an extrusive igneous rock.

• Igneous rock can also form as magma cools below earth's surface. These are called intrusive igneous rocks.

2. Sedimentary Rocks

• Sedimentary rocks are formed by years of sediment (small pieces of rocks/minerals) compacting together and becoming hard.

• A stream or river will carry lots of sediments to a larger body of water. These pieces will settle at the bottom and over a really long time (perhaps millions of years), they will form into solid rock.

• Some examples of sedimentary rocks are shale, limestone, and sandstone.

3. Metamorphic Rocks

• Metamorphic rocks are formed by heat and pressure.

• They are generally found inside the Earth's crust.

• Metamorphic rocks are often made from other types of rock. For example, shale, a sedimentary rock, can be changed into a metamorphic rock such as slate.

• Other examples of metamorphic rocks include marble and anthracite.

Any questions so far?

Multiple Choice

Which type of igneous rock is formed when lava erupts out of a volcano?

• Intrusive

• Extrusive

Multiple Choice

Which type of igneous rock is formed when magma cools beneath the earth's surface?

• Intrusive

• Extrusive

Multiple Choice

Which type of rock is formed when years of sediment is compacted together? (clue: use the names of the rocks to help you)

• Igneous

• Metamorphic

• Sedimentary

Multiple Choice

Which type of rock is formed by heat and pressure near the earth's crust?

• Igenous

• Metamorphic

• Sedimentary

The Rock Cycle

• The rock cycle is how natural processes (weathering, erosion, deposition, heat, and pressure) can cause rocks to change from one type to another.

• The process is very slow but is constant.

Weathering and Erosion

• Rocks on the surface of the earth are constantly being broken down by wind and water.

• The result of all this? Large rocks are worn down to smaller sediments.

• When the sediments are broken off a rock and stay in the same area, it is called weathering.

• When the sediments are carried somewhere else, it is called erosion.

Multiple Choice

________ occurs when sediments are broken off from a larger rock and stay in the same place.

• Weathering

• Erosion

Multiple Choice

________ occurs when sediments are broken off from a larger rock and are carried off.

• Weathering

• Erosion

Multiple Choice

________ occurs when sediments are broken off from a larger rock and are carried off.

• Weathering

• Erosion

Deposition

• Sediments are carried away by wind or by rain, streams, rivers, and oceans. As rivers get deeper or flow into the ocean, their current slows down, and the rock particles (mixed with soil) sink and become a layer of sediment. This is called deposition.

Compaction/Cementation

• As the layers of sediment stack up (above water or below), the weight and pressure compacts (squashes down) the bottom layers. This is called compaction and cementation.

• After years of this, the sediment turns into sedimentary rock.

Multiple Choice

Compaction/cementation of sediments forms which type of rock?

• Igneous

• Metamorphic

• Sedimentary

Metamorphism

• Metamorphism: Over very long periods of time, sedimentary or igneous rocks end up buried deep underground, usually because of the movement of tectonic plates. While underground, these rocks are exposed to high heat and pressure, turning them into metamorphic rock.

Multiple Choice

Metamorphism forms which type of rock?

• Igneous

• Sedimentary

• Metamorphic

Melting and Crystallization

• Melting: Metamorphic rocks underground melt to become magma. When a volcano erupts, magma flows out of it. 

• Crystallization of magma: As the lava cools it hardens and becomes igneous rock.

Any questions?

Let's try some sample test questions!

Multiple Choice

Which statement is true about rocks?

• Minerals are made of rocks.

• Crystals are made of rocks.

• Rocks are made of one or more minerals.

• Magma is made of solid rock.

Multiple Choice

Which type of rock is formed when particles (sediments) are compacted and cemented together?

• igneous

• metallic

• sedimentary

• metamorphic

Multiple Choice

In the rock cycle an igneous rock forms from

• cooling temperatures

• high pressure and heat

• weathering and erosion

• compacted plant remains

Multiple Choice

Which of these are parts of the geologic process that changes metamorphic rock into sedimentary rock?

• volcanic eruption and lava flow

• igneous intrusion and solidification

• faulting and displacement

• erosion and deposition

The End

Enjoy the Spring Break

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