1. Igneous Rocks

2. Fig. 7.16

3. Volcanic igneous rocks Plutonic igneous rocks
Complete the following table by identifying which of the characteristics in the left-hand column are present in volcanic and/or plutonic igneous rocks by stating yes or no for the appropriate number. One characteristic has been completed as an example.
Characteristic
Volcanic igneous rocks
Plutonic igneous rocks
May form from basaltic magma 1. 2.
Form at Earth’s surface 3. 4.
Have texture 
Made of small grains 5. 6.
Granite is an example 7. 8.
Form as a result of melting 9.
10.
Present at Earth’s surface only after erosion
11.
12.
Contains minerals
13.
14.
Classified based on color
15. 16
Dark-colored examples have low silica content 17
18.
Contain visible grains
19.
20.

4. Overview of Igneous Rocks
Koryakskaya
Sopka Volcano,
Eastern Russia
Form when minerals crystallize from magma
IntrusivePlutonic
ExtrusiveVolcanic
Magmas derived from below the Earth’s surface in the mantle
Magma is hot and buoyant

5. It’s all about heat and density
Heat source??
Geothermal Gradient
Composition
Hot stuff
Heat source = radioactive decay
Geothermal gradient = 25 deg C/km
Composition = heavier elements make heavier minerals/rocks
Hot Stuff = density of a material is dependent on temperature

6. Igneous Rock Classification
Composition
Texture
Felsic
Intermediate
Mafic
Ultramafic
Phaneritic
Granite
Diorite
Gabbro
Peridotite
Porphyritic Phaneritic
Porphyritic Granite
Porphyritic Diorite
Porphyritic Gabbro
Aphanitic
Rhyolite
Andesite
Basalt
Porphyritic Aphanitic
Porphyritic Rhyolite
Porphyritic Andesite
Porphyritic Basalt

7. Intrusive Vs. Extrusive
Plutonic
Formed within the Earth
Magma
Reach Surface by uplift and erosion of the Earth’s Crust
Volcanic
Formed at the Surface
Lava

8. Texture Related to the cooling history of the rock Other textures:
Really Fast = no grains glassy
Fast = Fine-grained aphanitic
Slow = Coarse-grained phaneritic
Complex = Mixture  porphyritic
Why??
Other textures:
Vesicular: trapped gases in lava
Pyroclastic: ash and rock fragments formed explosively

9. Texture Aphanitic Fine –grained Cooled quickly
Peanut Butter or
Sugar Cookie
Aphanitic
Fine –grained
Cooled quickly
Crystallized at the Earth’s surface
Porphyritic Aphanitic
Phaneritic
Porphyritic Phaneritic

10. Aphanitic--peanut butter cookie

11. Texture Porphyritic Aphanitic Aphanitic Two stages of cooling
Chocolate Chip Cookie
Aphanitic
Porphyritic Aphanitic
Two stages of cooling
1st cooled slowly within the Earth (larger cyrstals - Phenocrysts)
2nd cooled rapidly on the Earth’s surface (fine-grained matrix)
Phaneritic
Porphyritic Phaneritic

12. Porphyritic Aphanitic—Chocolate Chip Cookie

13. eaten the Oatmeal Cookie
Texture
Aphanitic
Porphyritic Aphanitic
Phaneritic
Coarse –grained
Cooled slowly
Crystallized within the Earth
Porphyritic Phaneritic
Ooopps!! I must have
eaten the Oatmeal Cookie

14. Phaneritic—Oatmeal Cookie

15. Texture Porphyritic Phaneritic Aphanitic Porphyritic Aphanitic
Oatmeal Raisin Cookie
Texture
Aphanitic
Porphyritic Aphanitic
Phaneritic
Porphyritic Phaneritic
Two stages of cooling
1st cooled slowly within the Earth (larger crystals - Phenocrysts)
2nd cooled faster but still slow enough that crystals fully develop – within the Earth (coarse-grained matrix)

16. Porphyritic Phaneritic—Oatmeal Raisin Cookie

17. Texture Vesicular –voids left by trapped gas Aphanitic
Porphyritic Aphanitic
Phaneritic
Porphyritic Phaneritic
Vesicular –voids left by trapped gas
Glassy
Pyroclastic

18. Texture Glassy Aphanitic Porphyritic Aphanitic Phaneritic
Porphyritic Phaneritic
Vesicular
Glassy
Very rapid cooling
Ions do not have time to from crystalline structures
Pyroclastic

19. Texture
Aphanitic
Porphyritic Aphanitic
Phaneritic
Porphyritic Phaneritic
Vesicular
Glassy
Pyroclastic – welded shards of rock & ash ejected from a vent during an eruption

20. Composition of Igneous Rocks
Silica (Si02) is primary ingredient of all magmas
Viscosity: Resistance to flow
Silica content
temperature
Rocks are made of minerals

21. Composition—Silica Content
Felsic: Feldspar & Silica
>65% silica  High Viscosity
Intermediate:
53-65% silica  Intermediate Viscosity
Mafic: Magnesium and Iron (Fe)
45-52% silica  Low Viscosity
Ultramafic:
<45% silica  Very Low Viscosity

22. Composition
Felsic-rhyolitic:
<900EC; Na, K, Al-rich
Light colored

23. Composition
Mafic-basaltic:
>1100EC; Ca, Fe, Mg-rich
Dark Colored

24. Composition Intermediate-andesitic: 900-1100EC; Na, Al, Ca, Fe, Mg, K
Salt & Pepper appearance
Andesite Porphyry
Diorite

25. Bowen’s Reaction Series
Melting
Crystallization
Hot
Cold
Different minerals crystallize from magmas at different temperatures

26. Magmatic Differentiation
Formation of more than one magma from a single parent magma

27. Magmatic Differentiation
Crystal Settling: crystallized minerals have a density greater than the magma and settle to the bottom due to gravity
Because Fe and Mg are first removed, melt becomes rich in SiO2, Na, and K
Marbles analogy

28. Magmatic Differentiation
Assimilation: magma reacts with the “country rock” which is adjacent to the magma chamber
Magma composition is altered according to the composition of the assimilated country rock
Inclusions are rocks Incompletely melted chunks of country rock

29. Magmatic Differentiation
Magma Mixing: Magmas of different compositions are mixed together
Resulting magma is of a composition intermediate between the parents

30. Magma Mixing

31. Magma Mixing

32. Magma Mixing

33. Fig. 7.21

34. Composition Quiz Which type of lava would flow most easily?
Mafic/Ultramafic
Which type of volcano would erupt most violently?
Felsic