1. Igneous Rocks
CH 3 Prentice Hall p

2. Igneous Rocks Form from lava or magma Made of mineral crystals
Classified according to:
Origin
Texture
Mineral Composition

3. Origin of Igneous Rocks
Classified according to where they formed.
Intrusive
Extrusive

4. Origin of Igneous Rocks
Intrusive
Forms when magma hardens beneath the Earth’s surface.
Granite
Makes up most of the continental crust.

5. Origin of Igneous Rocks
Extrusive
Forms from lava that erupted onto Earth’s surface.
Basalt
Forms much of the ocean crust.

6. Which is a way to identify if a rock is Igneous?
Streak B
Origin C
Solid D
Hardness

7. Igneous Rock Textures Slowly cooling, large crystals Example: Granite
Coarse Grained
Slowly cooling, large crystals
Example: Granite
Fine Grained
Lava cools quickly
Forms smaller crystals.
Porphyritic
Both textures – large AND small crystals.
Cools slowly, then rapidly.
No Crystals
Rock cools too quickly for crystals to form.

8. What is a Crystal?
A solid in which the atoms are arranged in a pattern that repeats again and again.

9. Igneous Rock Textures
Depends on the size and shape of it’s mineral crystals.
Coarse Grained
Porphyritic
Fine Grained
No Crystals

10. In your tray, what is the texture of sample…
Coarse-grained B
Fine-grained C
Porphyritic D
No visible crystals

11. Mineral Composition
Most of Earth’s rocks contain silica (silicon dioxide, SiO2)
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.

12. Igneous Rock Chart Low Density High Felsic (High) Silica Mafic (low)
Origin
Intrusive
(Magma)
Coarse Grained
Granite
Continental
Crust
Gabbro
Both
Porphyritic
Large crystals with
small crystals
Scattered on top.
Extrusive
(Lava)
Fine- Grained
Rhyolite
Basalt
Ocean
No Crystals
Pumice
Obsidian

13. Which rock likely has the most silica?B C

14. Igneous rocks are useful because they are hard, durable and dense
Uses of Igneous Rocks
Granite - building materials
Obsidian - sharp tools
Basalt - gravel, construction
Pumice - used for cleaning and polishing
Igneous rocks are useful because they are hard, durable and dense

15. 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

16. Silica Content Felsic Mafic Intermediate Basalt Gabbro Granite
Rhyolite
Mafic
Basalt
Gabbro
Intermediate
Diorite
Andesite