Igneous Rocks

staff.camas.wednet.edu

Igneous Rocks

Igneous Rocks

Chapter 4

Section 2


• Magma is molten rock

and becomes solid

when it cools.

• Magma comes from

deep below the earth’s

surface.

Magma


Magma (cont’d)

• It’s depths are ranging from near the surface

to about 150 km below the earth’s surface.

• Since magma is less dense than the solid

rock it’s forced upwards toward the surface.

• When magma reaches the surface it flows

out from volcanoes, then it becomes lava.


Intrusive Rocks

Rocks that form from

magma.

• Intrusive = interior

• Intrusive rocks are

only found at the

surface after layers of

rock and soil have

been removed by

weathering and

erosion.

• Slow cooling = large

mineral grains


• Extrusive rocks are

rocks that are formed

as lava cools on the

surface of the earth.

• exposure to air and

water, cools lava

quickly.

• quick cooling = small

mineral grains.

Extrusive Rocks


Volcanic Glass

Examples of Volcanic Glass

Volcanic Glass

Pumice Obsidian Scoria


Igneous Rock

Basaltic Granitic Andesitic


Classifying Igneous Rocks

• Basaltic Rock

– Dense, dark colored

– Magma is rich in iron and magnesium

– Poor in silica

– Lava is fluid and flows freely

– Black beaches of Hawaii


• Granitic Rocks

– Light-colored

– Lower denisty than basaltic rocks

– Magma is thick and stiff

– Contains lots of silica but low in iron and

magnesium

– Volcanoes can be explosive – built up gas

pressure


• Andesitic Rocks

– Mineral composition between granitic and

basaltic rocks

– Volcanoes can erupt violently

– Volcanoes form around Pacific Rim

More magazines by this user
Similar magazines