Chapter 3 Rocks and Minerals
Student Notes: Lesson 2 Igneous Rocks
Main Idea:
Different processes that take place on Earth form many different kinds of rocks. Igneous rocks may be
formed above the ground or below the ground.
Vocabulary:
Magma (152) – melted rock
Lava (152) – magma that reaches the Earth’s surface
Igneous rock (152) – rocks formed from melted rocks
How are igneous rocks formed?
Main Idea:
Igneous rocks are formed from magma or lava that cools and hardens.
Supporting Details
1. Below the Earth’s surface is a layer of melted rock called magma.
a. Magma can flow
b. When it reaches the Earth’s surface, it is called lava.
2. Igneous rocks are rocks that are formed when melted rock (magma/ lava) cools
3. Intrusive igneous rocks
a. Magma cools and hardens below the Earth’s surface
b. Magma, below the surface, takes a long time to cool
c. Because it takes a long time, large crystals are formed in intrusive rocks
4. Extrusive igneous rocks
a. Resulting from lava cooling and hardening above the Earth’s surface
b. Cools rather quickly resulting in small crystals. Not enough cooling time to make larger
crystals
What are the properties of some igneous rocks?
Main Idea:
Where an igneous rock is formed and its mineral make-up determine its properties.
Supporting Details
1. The properties of an igneous rock depend on the way it is formed and the mineral make-up.
a. Some igneous is hard; while other igneous easily crumbles
b. Size of the crystals give its texture
2. Properties of granite
a. is an intrusive igneous rock
b. has large mineral crystals giving it a coarse texture
c. made up of several mineral which give it variety of color
3. Properties of pumice
a. Is an extrusive igneous rock
b. Sometimes called lava rock
c. Tiny holes caused by gas escaping while the rock cooled
d. Very light
e. Crumbles easily
4. Properties of obsidian
a. Extrusive rock
b. Lava cooled in a few hours
c. Mineral crystals do not have time to form
d. Very smooth
e. Looks shiny like black glass
What are some of the uses of igneous rocks?
Main Idea:
Igneous rocks may have many important uses.
Supporting Details
1. Granite makes a strong and long lasting building material.
2. Gabbro is often mixed into concrete to make sidewalks, bridges, and buildings.
3. Soaps and other cleaners may contain pumic.