2. Earth Materials continued
Mineral
Naturally Occurring
Inorganic
Solid
Chemical Composition
Crystalline Shape

3. Rock
a coherent, naturally occurring solid, consisting of an aggregate of one or more minerals, or a mass of natural glass or organic matter.

4. Basic Rock Classifications
Igneous
Sedimentary
Metamorphic

5. Rock Cycle And Pressure Cementation Erosion/ Weathering
Sedimentary Rocks
Erosion/ Weathering
Sediment
Heat
Erosion/ Weathering
Erosion
Pressure
Heat and Pressure
Metamorphic Rocks
Igneous
Rocks
Heat
Cooling
Magma

6. ?
Define - Freeze ?

7. Igneous Rocks

8. Igneous Rocks Two types of igneous rocks
-a rock that forms when hot molten rock
(magma or lava) cools and freezes solid
Two types of igneous rocks
Plutonic – cools underground
Volcanic – cools above ground
Plutonic rocks cool very slowly because they are insulated by being buried several miles deep within the Earth. Because of this slow cooling, mineral grains have the opportunity to grow large enough to see without the aid of a magnifying glass. This course-grained texture is called “phaneritic”. [fan-er-it-ik].
Volcanic rocks cool near or at the surface of the Earth and therefore do not have mineral grains large enough to see, although sometimes there are some larger grains mixed into these fine-grained rocks. This fine-grained texture is called “aphanitic”, [af-a-nit-ik]. If there are some larger grains mixed in then the term “Porphyritic” is added.

9. Factors controlling Melting
1. Temperature:
Melt at [800oC and 1200oC]
Source of heat [radioactive decay]

10. Geothermal Gradient – the rate at which temperature increases with depth in the Earth
30OC/km

11. Norman Bowen

12. Bowen’s Reaction Series
Illustrates the order in which minerals crystalize from a magma
Liquid
The important concept to remember about this chart is:
- dark minerals tend to solidify first. Close to 1200 degrees C.
- light colored minerals tend to solidify last. Close to 800 degrees C.
- quartz is the last mineral to become solid.
- as solid rocks melt, the order is reversed. Quartz melts first and dark minerals melt last.
Solid

13. Iron and Magnesium rich
Dark colored minerals
Al, Ca, and Sodium rich
Light colored minerals

14. Factors controlling Melting
2. Pressure:
as pressure increases, melting temperature increases
as pressure decreases, melting temperature decreases
Lowering pressure causes melting in divergent margins.

15. Relationship between P, T, and Melt
Less Pressure
The blue and purple curves represent the melting temperature of dry basalt and granite and how it changes with depth.
More Pressure

16. Divergent Plate Boundary
The melting of rock at divergent plate boundaries is accelerated do to thinning of the crust which means there is less weight, or decompression.

17. Factors controlling Melting
3. Water content: As water content increases, melting temperature decreases

18. Now, compare the curve of dry granite to wet granite.
The presence of water during melting has a significant influence on melting temperature.

19. Water increases melting at convergent plate boundaries
Ocean water is introduced into the melting process as the subducting oceanic plate is pulled down under the continental plate.

20. Where do igneous rocks occur?
Most igneous rocks are found near plate boundaries, hot spots, and ancient regions of igneous activity.

21. Types of Molten Material
1. Magma – molten material below the Earth's surface
2. Lava – molten material above the Earth's surface

22. Magma Composition Changes
Partial melting
Assimilation
Magma Mixing
Fractional Crystallization
Molten oceanic crust and mantle material are low in silica (mafic) content compared to continental crust.
This means it has a low viscosity (it’s runny) and would create non-explosive volcanoes if it reaches to Earth’s surface.
As this mafic melt rises though the continental crust it can become silica rich (silisic) and therefore make an explosive volcano.

23. Partial Melting some minerals melt at a lower temperature than others.
As crust begins to melt, the light colored minerals (silisic, high in silica) will melt first. This early melt can flow away and what remains behind is mafic rich rock.

25. Assimilation – As mafic magma rises though silicic continental crust it’s chemistry changes to reflect the addition of silica. It becomes more viscous (sticky).
Magma Mixing – Magma from to different sources can meet up and mix together which will change the overall silica concentration.
Fractional Crystallization – As a body of begins to cool dark (mafic) minerals will line the chamber. The silica concentration in the remaining magma will increase.

26. Magma Viscosity
Viscosity – resistance to flow honey – high viscosity water – low viscosity
Viscosity increases as silica content increases.

27. Magma Chemistry
Molten material can consist of liquid rock, mineral grains and gases (H2O, CO2, SO2).
Silicon and oxygen (SiO2) make up the majority of magma
45% SiO2 - "low" silica content
75% SiO2 - "high" silica content
An igneous rock such as basalt is considered low in silica even though it has up to 45% silica in it. As it solidifies from a magma the silica is all incorporated into minerals. There is no silica left over to form the mineral quartz.
In high silica igneous rock quartz is formed.

28. Endmember Magma Chemistry
Mafic – low SiO2 / high iron, magnesium
Silicic – high SiO2 / high aluminum, calcium, sodium

29. Igneous Rock Types
Intrusive (plutonic) rock – cools and solidifies below the Earth's surface.
Extrusive (volcanic) rock – cools and solidifies above the Earth's surface.

30. Textures of Igneous Rocks
Texture – overall appearance, related to size, shape, and arrangement of minerals.
Texture is related to cooling history of an igneous rock, not its chemistry.

31. Textures of Igneous Rocks1.
Aphanitic (fine grained)
Lava
Earth’s surface 2.
Phaneritic (course grained)
Magma

32. All the terms on the left describe grain size which reflects the cooling rate.
The terms across the top describe changing chemistry (silica content)

33. Aphanitic Texture – Rapid Cooling Small Crystals

34. Phaneritic Texture – Slow Cooling Large Crystals

35. Silicic Chemical Composition
Phaneritic Texture –
Slow Cooling
Large Crystals
Aphanitic Texture –
Rapid Cooling
Small Crystals
Granite
Rhyolite

36. Intermediate Chemical Composition
Phaneritic Texture –
Slow Cooling
Large Crystals
Aphanitic Texture –
Rapid Cooling
Small Crystals
Diorite
Andesite

37. Mafic Chemical Composition
Phaneritic Texture –
Slow Cooling
Large Crystals
Aphanitic Texture –
Rapid Cooling
Small Crystals
Gabbro
Basalt

38. PHANERITIC texture
It means that the size of all grains in the rock are large enough to be distinguished with the unaided eye

39. APHANITIC texture
It means that not all grains in the rock are large enough to be distinguished with the unaided eye. Most of the rock is background mass.

40. Pegmatites

41. Ingersoll Mine
Ingersoll mine, Pennington Co., South Dakota, United States
One of the many adits at the old Ingersoll pegmatite. Private and Very dangerous. No Trespass.

42. Glassy Texture - Very Rapid Cooling - No Crystal Structure

43. Pyroclastic Texture
Ash Fall
Ash Flow

44. Plutonic Structures

45. Plutonic Structures

46. Image courtesy of geoinfo.nmt.edu