1. Definition, Classification, Formations
Igneous Rocks
Definition, Classification, Formations

2. Igneous Rocks: Outline
Rocks in General
Intro. to the Rock Cycle
Definition of an Igneous Rock
How igneous rocks “fit in” the Cycle
Classification of an Igneous Rock
Crystal Size and Implications
Composition and Implications
Igneous Rock Formations
Intrusions
Other

3. What is rock? Rock = collection of minerals
i.e., several natural, pure compounds in a solid mixture
Type of rock depends on process of formation

4. Intro. to the Rock Cycle

5. Igneous Rocks: Definition
Igneous rocks are solidified from hot liquid materials
i.e., cooled from magma OR lava

6. Igneous Rocks: Classification
Classified by two criteria
“Texture”: size of the crystals
three distinctions (see upcoming slides)
Composition: the minerals present in the rock
especially how much SILICA (i.e., SiO2)
multiple distinctions (see upcoming slides)

7. Texture Vocabulary Crystal Size involves three main distinctions
Coarse Grained Fine Grained No Crystals

8. Rock Cycle: What Can Texture Tell Us?

9. Texture Indicates Cooling Time
Intrusive Igneous Rocks
Extrusive Igneous Rocks
Cooled from magma under the surface
Can take millions of years
Coarse grains
Cooled from lava above the surface
from volcanoes, e.g.
Can cool in a few days or even minutes
Fine grains or no crystals

10. Porphyry – Mix and Match! What could cause coarse AND fine grains?

11. Composition Vocabulary
More Silica = Felsic
Less Silica = Mafic
Usu. more iron and magnesium
Other distinctions
Intermediate
Ultramafic!
FELSIC IS LIGHT almost always
MAFIC IS DARK

12. What Composition Tells Us
More silicates (felsic) are more viscous when liquid
i.e., they resist flow and cause different formations
Less silicates (mafic) are denser
may indicate the source of the magma/lava

13. Six Common Igneous Rocks (In Words)
Texture →
Composition ↓
Fine-Grained
Coarse-Grained
Felsic (High Silica)
Rhyolite
Granite
Intermediate (Mid Silica)
Andesite
Diorite
Mafic (Low Silica)
Basalt
Gabbro

14. Six Common Igneous Rocks (In Pictures)
Texture →
Composition ↓
Fine-Grained
Coarse-Grained
Felsic (High Silica)
Intermediate (Mid Silica)
Mafic (Low Silica)

15. Igneous Rock Formations: Intrusions
Intrusions form from intrusive rock
Can take millions of years to form, followed by a very long time to surface
Types that we study:
Batholiths
Stocks
Laccoliths
Dikes
Sills

16. Batholiths and Stocks Batholith from Greek, “deep rock”
HUGE intrusions
form deep in the Earth’s crust
most are granite
Stocks are just smaller versions (may be tip of a batholith)

17. Laccoliths and Dikes Laccolith from Greek, “pond rock”
magma intrudes into a space, causing layers of rock to bulge into an arch
Dikes are thin intrusions that cut across layers

18. Examples http://en.wikipedia.org/wiki/File:Laccolith_Montana.jpg

19. Sills Intrusions that get in between layers
Resemble laccoliths, but remain flat (no arch)

20. Example

21. Igneous Rock Formations: Extrusions
Lava Plateaus
Layers of lava that have built up
Formed as lava flows over flat areas
Any volcanoes are also extrusions (details in a later unit)

22. Example
A JOEL BARTON ORIGINAL!