1. Igneous Rocks Igneous Rocks “Ignis” means fire
Rocks that are formed from cystallization of magma
Magma is molten rock
Lava is magma that is on the Earth’s Surface

2. Igneous Rocks Two Types of Igneous Rocks Extrusive (Exterior)
Intrusive (Interior)
Igneous rocks that solidify into rock beneath Earth’s surface
Coarse Grained
Cool Slowly
Granite

3. Extrusive Igneous Rocks
Extrusive (Exterior)
Igneous rocks that solidify into rock on Earth’s surface
Fine Grained
Cool Quickly

4. Intrusive Igneous Rocks
Intrusive (Interior)
Igneous rocks that solidify into rock beneath Earth’s surface
Coarse Grained
Cool Slowly
Granite

5. Igneous Rock Formation

6. Origin of Magma Where does the heat come from that melts rocks?
Formation of Earth
Heat from the decay of radioactive elements

7. Factors that Affect Magma Formation
Temperature
Increases with depth
Pressure
Water Content
Decreases melting point
Mineral Composition
Different minerals, different melting points

8. Characteristics of Magma
Slushy Mix of molten rock, gases, and mineral crystals
Common Elements
Oxygen (O)
Silicon (Si)
Aluminum (Al)
Iron (Fe)
Magnesium (Mg)
Calcium (Ca)
Potassium (K)
Sodium (Na)
Compounds in Magma
Silica ( Si02)
Most abundant
Greatest effect on Magma Characteristics
Effects melting temp
Viscosity of Magma
Types of Magma
Based on amount of Silica
Basaltic
Andesitic
Rhyolitic

9. Type of Magma
SiO2 Content
Rhyolitic
70%
Andesitic
60%
Basaltic
50%

10. Melting Rocks Question
Does a rocks melt like an ice cube, all at the same time?

11. Melting Rocks Rocks melt according to their melting points.
Example: Ice cube with wax
Which would melt first ice or wax?
This example is known as partial melting.
Partial Melting: some minerals melt at lower temperatures and other minerals remain solid
Think of “stew”

12. Fractional Crystallization
Opposite of Partial Melting
Last to melt are first to solidify (crystallize)

13. Bowen’s Reaction Series
N.L. Bowen
Canadian
1900’s
Stated that “as magma cools, minerals form in predictable patterns”
Known as Bowen’s Reaction Series

14. Bowen’s Reaction Series
Two Branches
Feldspars
Continuous, gradual change of mineral compositions
Iron-Rich Minerals
An abrupt change of mineral type

15. Bowen’s Reaction Series

16. Feldspars Continuous Change First Feldspars are rich in Calcium (Ca)
Sodium (Na) increases as cooling continues
Last Feldspars to form are Sodium rich (Na)

17. Iron Rich Minerals Discontinuous Change
Magnesium (Mg) cools around 18000C, when olivine crystallizes, this continous up to 15570C.
Now Pyroxene begins to form. All olivine that was formed is now turned to pyroxene
Quartz is the last to form, because silica and oxygen are the last to crystallize

18. Why do we find Olivine?

19. Four main groups of igneous rocks based on magma type/mineral composition
Felsic: high silica content, light colored, from thick & slow moving magma, contains low amounts of Ca, Fe, and Mg dominant minerals quartz, potassium rich feldspar
Ex: granite, pumice, rhyolite
Magma Type:
Intermediate: moderate amount of silica, mixture of colors dominant minerals: sodium and calcium rich feldspar
Ex: andesite, diorite
Mafic: low silica content, dark colored, high levels of Fe & Mg formed from thinner, more fluid, & hotter magma than Felsic rocks dominant minerals hornblende, calcium rich feldspar
Ex: basalt, gabbro
Ultramafic: very low silica content, dark colors, high levels of Fe & Mg dominant minerals: olivine, pyroxene
Ex: peridotite, dunite

20. Classifying Igneous Rocks
Igneous rock textures:
Crystal size is dictated by the rate of cooling of the magma body. A slower cooling rate results in larger mineral crystals being formed in the rocks as they cool.
Porphyritic texture - Large crystals surrounded by fine grained rock. The rock initially cools slowly to form some large crystals and then cools quickly to form the fine grained rock surrounding them.

22. The Scheme for Igneous Rock Identification

23. A Brief Tour

24. Grain Size
Description
Crystal size

25. Igneous rocks have “Intergrown Crystals”

26. Intergrown

27. Intergrown

28. Intergrown

29. Not Intergrown

30. Where it was formed Outside the volcano: Extrusive
Inside the Earth: Intrusive

31. Bubbles?
Yes= Vesicular

32. Bubbles?
No=Non-vesicular

33. Color Neither Light nor Dark Very Light NotVery Light Not Very Dark
Darkest
Lightest

34. Density
Medium Density
Very Light
Light
Dense
Very Dense

35. Finding The Minerals Unless you have other information,
work in the middle of the rock’s box.
Identify the rock.

36. This is the amount of Potassium Feldspar in the rock.

37. This is the amount of Quartz in the rock.

38. This is the amount of Plagioclase Feldspar in the rock.

39. Use tick marks on a scrap paper to measure the percentage.
Potassium Feldspar 25%
Quartz 40%

40. Name a light-colored, fine-grained
rock with no bubbles.
Practice

41. Name a coarse-grained, dense rock.

42. Igneous Rock Resources
Ore Deposits
Building Materials
Other Uses

43. Ore Deposits
Veins: streaks of valuable metal within a mineral. Created when a metal-rich fluid, such as gold-quartz, goes through fractional crystallization, the mineral (quartz) has a lower crystallization temp and thus solidifies before the gold. The gold remains liquid and settles between the quartz crystals forming “gold veins.”
Pegmatites: veins with extremely large grain crystals. Creates some of the world’s most precious gems.
Kimberlites: intrusions of magma cooled deep within earth’s crust. Usually find diamonds with kimberlites. Named after location of first discovery, Kimberly, South Africa.

44. Building Materials
Many IR’s are used in building materials because of their interlocking crystals strength
IR’s are fairly weather resistant
Ex: Granite – building
Ex: Basalt – crushed up to make gravel

45. Other Uses Pumice – cleaning and polishes Obsidian
heated to make perlite, a soil additive that keeps soil loose.
scalpels – more precise and smoother than steel, but 10x the cost