Igneous Rocks

Igneous RocksCH 3 Prentice Hall

p. 78-81CH 3 Prentice Hall

p. 78-81

• Form from lava or magma• Made of mineral crystals• Classified according to:– Origin– Texture– Mineral Composition

Igneous Rocks

• Classified according to where they formed.

Intrusive Extrusive

Origin of Igneous Rocks

Intrusive

• Forms when magma hardens beneath the Earth’s surface.• Granite• Makes up most of

the continental crust.

Origin of Igneous Rocks

Extrusive

• Forms from lava that erupted onto Earth’s surface.• Basalt

• Forms much of the ocean crust.

Origin of Igneous Rocks

A

•Streak

B

•Origin

C

•Solid

D

•Hardness

Which is a way to identify if a rock is Igneous?

Igneous Rock Textures

•Slowly cooling, large crystals

•Example: Granite

Coarse Grained

•Lava cools quickly

•Forms smaller crystals.

Fine Grained

•Both textures – large AND small crystals.

•Cools slowly, then rapidly.

Porphyritic

•Rock cools too quickly for crystals to form.

No Crystals

• A solid in which the atoms are arranged in a pattern that repeats again and again.

What is a Crystal?

• Depends on the size and shape of it’s mineral crystals.

Igneous Rock Textures

Coarse Grained Porphyritic Fine Grained

No Crystals No Crystals

A

•Coarse-grained

B

•Fine-grained

C

•Porphyritic

D

•No visible crystals

In your tray, what is the texture of sample…

• Most of Earth’s rocks contain silica (silicon dioxide, SiO2)

Mineral Composition

High Silica (Felsic)

• Forms light colored rocks.• Granite

• Dark to light gray, red and pink.

Low Silica (Mafic)

• Forms dark colored rocks.• Basalt

• Contains dark colored minerals. No quartz.

Igneous Rock Chart

Origin

Intrusive

(Magma)

Coarse

Grained

GraniteContinental

CrustGabbro

Both Porphyritic

Large crystals with small crystals

Scattered on top.

Extrusive

(Lava)

Fine- Grain

edRhyolite

BasaltOcean

Crust

No Cryst

als Pumice Obsidian

Low Density HighFelsic (High) Silica Mafic (low)

A B C

Which rock likely has the most silica?

Granite - building materials

Obsidian - sharp tools

Basalt - gravel, construction

Pumice - used for cleaning and polishing

Uses of Igneous Rocks

• Igneous rocks are useful because they are hard, durable and dense

Class Work

• Examine 5 Igneous Rocks and write down their texture–(Fine-grain, Coarse-grain, Porphyritic,

No Grain)• Read the textbook, pages 78-81–Answer Questions 1 – 4 on page

Silica Content

• Felsic– Granite– Rhyolite

• Mafic–Basalt–Gabbro

• Intermediate– Diorite– Andesite