1. Rock Notes

3. 3 types of Rocks
Igneous
Metamorphic
Sedimentary

4. Igneous Rocks formed from the crystallization of magma
Intrusive - Coarse grained igneous rocks that cool slowly beneath the Earth’s surface
Extrusive - Fined grained igneous rocks that cool quickly on the Earth’s surface

5. Composition of Magma
Often a slushy mix of molten rock, gases, and mineral crystals
O, Si, Al, Fe, Mg, Ca, K, Na
Magmas are classified as basaltic (70%), andesitic (60%), and rhyolitic (50%), based on the amount of (SiO2)
Silica determines melting temp and how quickly magma flows

6. Origin of Magma Upper mantle and lower crust Main factors Temp
Pressure
Water content
Mineral Composition

8. Bowen’s Reaction Series
See handout
Mafic is used for silicate minerals, magmas, and rocks which are relatively high in the heavier elements
Felsic is used for silicate minerals, magmas, and rocks have a lower percentage of the heavier elements, and are correspondingly enriched in the lighter elements, such as silica and oxygen, aluminum, and potassium.

9. Classifying Igneous Rocks
Grain Size
Cooling rates determine
Texture
Fine grained
Cannot see/need a microscope
Coarse Grained
Able to see grains with the naked eye
Porphyritic
2 or more different sizes of mineral grain

10. Metamorphic
Causes – During metamorphism a rock changes form while remaining solid
Heat
Pressure

11. Types of Metamorphism
Regional
Contact
Hydrothermal

12. Regional Metamorphism
Process that affects large areas of Earth’s crust, producing belts classified as low, medium, or high grade, depending on pressure on the rocks, temperature, and depth below the surface

13. Contact Metamorphism
Molten rock comes in contact with solid rock
High temp and moderate to low pressure

14. Hydrothermal Metamorphism
When very hot water reacts with rock and alters its chemistry and mineralology

15. Metamorphic textures Foliated Nonfoliated Porphyroblasts
Wavy layers and bands of minerals
Nonfoliated
Lack mineral grains in one direction
Quartzite and marble
Porphyroblasts
Crystals resemble the very large crystals found in porphyritic igneous rocks but form not from magma in solid rock by the reorganization of atoms during metamorphism

16. Sedimentary Rocks Formation
Sediments from weathering of preexisting rocks and that is what we see on the ground
Rocks get cemented together by lithification

17. Burial and Lithification
The physical and chemical processes that transform sediments into sedimentary rocks
Cementation – temps become warm enough to start chemical and mineral changes that cause mineral growth between spaces in sediments causes the formation of the new rocks
CaCO3, Fe203

19. Features of Sed. Rocks Stratification – Layering of sediments
Graded-bedding
Cross-bedding
Ripple Marks – Action of wind or water on sand
Mud cracks – muddy deposits dry and shrink
Concretions - geodes

31. Types of Sedimentary Rocks
Clastic
Chemical
Organic

32. Clastic - Classified by size of the sediments they contain
Conglomerate – Rounded gravel
Breccia – sharp angular gravel
Sand sized Particles
Shale – Clay sized particles

33. Chemical Sed. Rocks Evaporates
Water evaporates and leaves behind the minerals dissolved in the water
Examples:
Gypsum and halite

34. Organic Sed. Rocks
Made from living things
Coal and Limestone

35. Why are they Important? Energy Resources
Coal, crude oil, natural gas, water, salt, iron ore
Helps in knowing the provenance (i.e. source area of the sediments); change in climatic conditions i.e. in knowing and understanding old climate=paleoclimate
Fossils are found in sedimentary rock

36. Sedimentary Rocks are classified by the Clastic sediments they are broken into.
This system describes rock and mineral fragments produced by weathering and erosion and classified according to particle size and shape.

37. Wentworth Size Scale Boulder >256 mm Cobble 64-256 mm Pebble
Conglomerate
Cobble mm
Pebble
2-64 mm
Sand
1/16-2 mm
Sandstone
Silt
1/256-1/16 mm
Siltstone
Clay
<1/256 mm
Shale

38. Weathering of Rocks
The change in the physical form or chemical composition of rock materials exposed at the Earth’s surface

39. Chemical Weathering
Occurs when the minerals in a rock are dissolved or otherwise chemically changed
The weaker minerals are broken down and weakens the rock allowing for stronger minerals to break off

41. Hydrolysis

42. Mechanical Weathering
Minerals remain chemically unchanged
Rock fragments simply break off
Joints – long curved cracks parallel to the surface of rocks
Exfoliation – peeling off in layers, causing jagged edges or rock to become smooth

45. Agents of Weathering
Water
Wind
Ice
Organic Activity
Abrasion

46. Water On the Beach Rivers, Waterfalls
Rainwater and runoff pulls sediments away

47. Wind
Wind blows sand and erodes surfaces

48. Ice
Glaciers - Break apart rocks and gouge out valleys
Ice Wedging
Occurs when water seeps into cracks or joints in rock and freezes
Water volume increases by 10% when frozen
Commonly occurs at high elevations and where climate temps vary

53. Organic Activity Plants root themselves in joints
Animals burrow in rocks and soil
Some Plants produce acids

55. Abrasion
Collision of rocks with one another, resulting in the breaking and wearing away of the rocks
Can happen on beach, in water or wind, rolling down mountains

56. Erosion
Process by which the products of weathering are transported

57. Deposition
Alluvial Fans
Deltas
Soil

59. Resource Page Pictures and information found at www.geologyrocks.co.uk