Igneous RockSeptember 12, 2011

Is That a Fact!Igneous rocks that form deep

underground are called plutonic rocks, after Pluto, the god of the underworld in Roman mythology.

Volcanic rocks are named after Vulcan, the Roman god of

metalworking and fire.

Do you think rock that cooled & solidified from lava on Earth’s surface would look different from those that cooled & solidified from magma inside the earth?

Why? Write your thoughts in your Science Journal.

Bellringer

Do you think rock that cooled & solidified from lava on Earth’s surface would look different from those that cooled & solidified from magma inside the earth?

When magma cools slowly, under the Earth, large well-developed crystals form; but when magma erupts onto the surface as lava, it cools more quickly where there is not enough time for large crystals to grow.

Bellringer

Objectives

1. Describe three ways that igneous rock forms.

2. Explain how the cooling rate of magma affects the texture of igneous rock.

3. Distinguish between igneous rock that cools within Earth’s crust & igneous rock that cools at Earth’s surface.

1. Rock is heated2. Pressure is released3. Rock changes composition

Three ways igneous rock forms

Felsic rocks-Light colored & less dense than dark colored rocks. Made of Al, K, Si, & Na.Page 794 Periodic Table of the Elements

Mafic rocks-Dark colored & more dense than light colored rocks. Made of Ca, Fe, & Mg.

Longer it takes to cool, the more time the crystals have to grow.

Cooling rate of magma

The larger the crystals are the coarser the texture of the igneous rock.

In contrast, the faster the rock cools, the crystals are fine-grained due to the igneous rock containing smaller crystals.

Texture of igneous rock

Using the Figure◦Page 99 Figure 2.◦Rank the rocks by how fast they cooled.◦#1 being the fastest cooled & #4 being

the slowest cooled◦(Pay attention to the grain size of each

rock.)

Igneous rock that cools & solidifies within Earth’s crust

Usually has a coarse-grained texture Minerals within are large, visible crystals

Intrusive Igneous Rock

Igneous rock that forms from lava & cools at or near the Earth’s surface.

Fine-grained igneous rock Contains very small or no crystals at all

Extrusive Igneous Rock