1

Igneous Rocks

Vanderbilt Student Volunteers for Science

Fall 2013

2

Introduction• There are 3 types of rocks:

– Sedimentary– Metamorphic– Igneous

What are igneous rocks?• Igneous rocks form when

the melted rock material from inside the Earth cools.

• This cooling and hardening of melted rock material can occur both on and underneath the Earth’s surface

Pass out the Volcano Handout Refer to its images as you discuss key terms

Introduction

Lava Magma

3

Extrusive Rock Intrusive Rock

Extrusive igneous rocks: formed from lava on or above the Earth’s surface.

Intrusive igneous rocks: formed from magma underneath the Earth’s surface.

Melted rock on or above the Earth’s surface.

Melted rock underneath the Earth’s surface.

VS

VS

4

Examining Igneous Rocks

A. Intrusive vs. extrusive igneous rocks1. Hand out the igneous rock

mats and igneous rock samples

2. Have students place rocks on corresponding spots on the mat. Help them as needed.

3. Explain that all these rocks are igneous, and show which are extrusive and which are intrusive

5

Examining Igneous Rocks4. Ask students:

1. What differences do you see between the intrusive and extrusive igneous rocks?Extrusive are solid colors while intrusive are ‘speckled’

2. What are the differences among the 3 columns?Color from left to right gradually gets lighter

5. Explain the columns:1. Blue: Felsic rocks – contain

silicon, sodium, aluminum, potassium

2. Red: Mafic rocks – contain calcium, iron, magnesium

3. Gray: Contains minerals found in both felsic & mafic rocks

6

Examining Minerals of Igneous Rocks

B. The minerals of igneous rocks1. Remind students that minerals

are the building blocks of rocks2. Hand out the mineral rock sets

and magnifying glasses3. Explain the Venn diagram:

1. Blue circle: minerals found in a felsic/granite rock

2. Gray circle: minerals found in an intermediate rock

3. Red circle: minerals found in a mafic/basaltic rock

4. Overlapping areas: minerals are found in both types of igneous rocks

7

Examining Minerals of Igneous Rocks

4. Ask students:1. What differences in color do

they see?Color gets lighter from left to right

2. What is the relationship between the color of the mineral and the color of the rocks?Color of rock depends on color of minerals that make it up

3. Which type of igneous rock (extrusive or intrusive) is it easiest to identify the minerals that make it up?Intrusive because you can see the different crystals

5. Spend 3 minutes examining the rocks to find minerals.

Examining Pegmatite

1. Hand out pegmatite samples– Pegmatite is igneous rock with

large mineral crystals. It does not have a specific mineral composition.

2. Have students identify what type of igneous rock their sample of pegmatite is by:1. Based on its appearance,

decide if it is intrusive or extrusive

2. Closely examining the minerals in the pegmatite

3. Based on minerals they can identify, determine whether it is granitic, intermediate, or basaltic

Answer: Intrusive rock (large crystals)Felsic or intermediate (depending on minerals seen)Granite or Diorite

9

Special Types of Volcanic Rocks

1. Tell students they will look at special volcanic rocks, which are different from the igneous rocks that they have already looked at

2. Hand out volcanic rocks and volcano diagram.

3. Tell students to make observations about each rock, and to fill in their observation sheets

4. Working through each rock, discuss the students’ observations and what makes each rock unique

5. Collect all rocks and put them into the corresponding cases in the labeled positions