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Definition, Classification, Formations

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Presentation on theme: "Definition, Classification, Formations"— Presentation transcript:

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!


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