1. Igneous Rocks c. Classify rocks by their process of formation.
d. Describe processes that change rocks and the surface of the earth.

2. Igneous Rock Identified by origin, texture, and mineral composition.
From the Latin word “ignis,” which means fire.
Tend to have average densities.

3. form from the cooling of molten rock (lava and magma).
Igneous Rocks
form from the cooling of molten rock (lava and magma).

4. Are lava and magma the same?
LAVA is molten material found on the surface of the earth.
MAGMA is molten material found beneath the surface of the earth.

6. Igneous rock Extrusive Rock Intrusive rock At or near surface
Inside Earth
Lava
Magma
Cools fast
Cools slowly
Fine Grained
Coarse-grained
Small Crystals
Large Crystals

7. Classified by Formation:
Extrusive Rock is formed from lava.
Magma Exits the Earth to form lava at the surface.
(Basalt)

8. Extrusive Igneous Rock

9. Classified by Formation:
Intrusive Rock is formed when magma hardens beneath Earth’s surface.
Inside the Earth
(Granite)

10. Intrusive Igneous Rock

11. TEXTURE TEXTURE reflects cooling rate of magma or lava.
RAPID COOLING = SMALL(fine) Crystals
RAPID COOLING = VOLCANIC
SLOW COOLING = LARGE (coarse) Crystals
SLOW COOLING = PLUTONIC

12. Classified by Texture:
Fast Cooling Lava (Extrusive)
Fine-Grained, small crystals, smooth
Slow Cooling Magma (Intrusive)
Coarse-Grained, large crystals, rough

13. Types of Grain Size (texture)
Aphanitic
Phaneritic
Glassy

14. Aphanitic (fine grained) = grains are very fine
Grain Size
(Texture)
Aphanitic (fine grained) = grains are very fine
-such rocks are formed when the rock solidifies at or near the surface (extrusive)
Small crystals < 2 mm
Fast cooling rates

15. Rhyolite
Felsite

16. Basalt
Scoria

17. TEXTURE Types of Textures
Phaneritic (coarse grained) = large, identifiable crystals
-are formed when rocks solidified far below the surface (intrusive)
Large crystals > 2 mm
Slow cooling rate =
Plutonic (formed in a pluton – a cave of magma within the volcano)

18. Examples

19. TEXTURE Types of Textures
Glassy = crystal formation does not occur
-rocks are formed when molten rock is suddenly ejected from a volcano
No crystals, lava cools too fast
Extremely fast cooling rate =
Obsidian

20. An intrusive igneous rock would have what type of texture? Why?
Coarse-Grained, large crystals. Smooth & rough.
It is hotter in the earth than on the outside of the earth so it takes longer for magma to cool down.

21. An extrusive igneous rock would have what type of texture? Why?
Fine-Grained or glassy texture
It is cooler on the surface of the Earth so the rocks can cool faster.

22. MINERAL COMPOSITION You can determine basic igneous rock composition
just by the COLOR of the rock.
DARK COLORED igneous rocks = MAFIC
LIGHT COLORED igneous rocks = FELSIC
GRAY COLORED igneous rocks = INTERMEDIATE

23. Felsic Igneous Rock
Lighter colored igneous rocks will have lots of silica.
They tend to be less dense than the darker versions.

24. Mafic Igneous Rocks
Less silica means these rocks will be darker than their felsic counterpart.
They will be denser also.