1. Notes
Igneous Rock

2. Think About…
How can two rocks made of the same minerals look very different?

3. Magma vs Lava
Deep inside Earth, temperatures are hot enough (750 to 1250 degrees C) to melt rock.

4. Magma vs Lava Molten rock inside Earth is called magma.
Molten rock that reaches the surface is called lava.

5. Magma and Lava
Rock formed from magma can have the same minerals as a rock formed from lava, but they will have different crystal structures and different names.

6. Intrusive vs Extrusive
Igneous rocks are classified based on its minerals and the size of its crystals (also called: grain size or texture)

7. Intrusive vs Extrusive
Intrusive igneous rock forms when magma cools inside Earth.
Example: Granite (made of Quartz, Feldspar, and Mica)

8. Intrusive vs Extrusive
Extrusive igneous rock forms when lava cools on Earth’s surface.
Example: Rhyolite (made of Quartz, Feldspar, and Mica)

9. Intrusive vs Extrusive
Granite and rhyolite have the same minerals (Quartz, Feldspar, Mica) but were formed in different ways.

10. Texture
Texture (of an igneous rock)- the size of its mineral crystals (also called grain size).

11. Texture
Large crystals form in intrusive igneous rock because:

12. Texture Inside Earth is very hot
High temperatures make the magma cool slowly
Slow cooling allows time for large crystals to form

13. Texture
Very small crystals form in extrusive rocks because…

14. Texture The surface of Earth is cooler.
Lower temperatures cause lava to cool quickly.
There is no time for large crystals to form.

15. Identifying Igneous Rock
To identify igneous rocks, you can look at texture and mineral composition.

16. Identifying Igneous Rock
Most igneous rocks are made up of silicate minerals.

17. Identifying Igneous Rock
Silicate minerals contain silica, a mixture of silicon and oxygen.

18. Identifying Igneous Rock
Geologists sometimes classify igneous rocks based on how much silica they have.

19. Identifying Igneous Rock
You can estimate how much silica is in an igneous rock by looking at its color.

20. Identifying Igneous Rock
Igneous rocks with a lot of silica are light in color.
Examples: granite and rhyolite

21. Identifying Igneous Rock
Igneous rocks with little silica are dark in color.
Examples: Gabbro and basalt

22. Landforms
A landform is a natural feature on Earth’s land surface.

23. Landforms
Ship Rock in New Mexico is an example of a landform made of igneous rock.

24. Landforms
As hot magma pushes toward Earth’s surface, it makes formations underground.

25. Landforms
When the rock above the formation wears away, we have intrusive rock on the surface.

26. Landforms
When magma reaches Earth’s surface before cooling, the lava can erupt in different ways.

27. Landforms
Lava that has very little silica flows easily and spreads out in thin sheets.

28. Landforms
Lava that has a lot of silica does not flow easily, and usually results in violent eruptions.

29. Review
Geologists classify an igneous rock on the basis of its crystal size and the amount of ______ its minerals contain.
Carbon
Silica
Sediment
Foliation

30. Review
2. What kind of texture would obsidian (an igneous rock) have if it cooled very quickly while it was being formed?
Multicolored and banded
Smooth and shiny with no visible grains
Coarse grains
Made up of jagged grains

31. Review
3. What is the classification of a rock formed inside Earth with large, visible grains?
Intrusive igneous
Sedimentary
Metamorphic
Extrusive igneous