1. Rocks and The Rock Cycle

2. A. Rocks- any solid mass of mineral or mineral-like matter that occurs naturally as part of our planet B. There are 3 major types or families of rocks: 1. Igneous rocks 2. Sedimentary rocks 3. Metamorphic rocks

3. II. Igneous Rocks A. How Igneous Rocks are formed 1. Magma- molten material underground 2. Lava- magma that reaches the surface 3. Igneous rocks are formed from magma that has cooled and hardened either beneath the surface or from a volcanic eruption

4. B. Formation processes influence Igneous Rock types - Magma contains some gases, including water vapor- this make it less dense, so it rises - As magma rises, it cools and forms crystals - The longer the cooling time the larger the crystals

5. 1. Intrusive Igneous Rocks - Form when magma hardens beneath Earth’s surface - Magma intrudes into existing rocks - Typically see crystals 2. Extrusive Igneous Rocks - form when lava hardens on the surface of the Earth - Extruded onto the surface - Typically don’t see crystals Granite Rhyolite

6. C. Classification- Igneous rocks are classified by texture and composition 1. Texture refers to the appearance of an igneous rock crystals a. Coarse- grained Texture- form as a result of slow cooling, ions can move = large crystal size; example: granite

7. b. Fine-grained Texture- form as a result of quick cooling time, ions lose motion= small crystal size; example: basalt c. Glassy Texture- form from lava that cools rapidly, ions don’t have time to arrange = glassy texture; example: Obsidian

8. d. Porphyritic Texture- rocks with different size minerals that form from varying cooling rates; example: Andesite 2. Composition refers to the proportions of light and dark minerals in the rock a. Granitic Composition- contain mainly quartz and feldspar. Make up major rocks of continental crust

9. b. Basaltic Composition- contain mainly dark colored minerals. -Darker and denser than granitic composition - Make up the ocean floor

10. Box of Rocks- Igneous Rocks

11. 1. Radioactivity- in atoms that are unstable, the nuclei spontaneously break apart or decay. - The radioactive isotope is known as the parent, product is known as the daughter isotope D. Dating With Radioactivity

12. 2. Radioactive Dating- rates of decay for certain isotopes have been measured and DO not vary in Earth’s outer layers - Parent isotopes decay at a constant rate since the formation of the rock they are in - The decay product has also been accumulating at a constant rate

13. 3. Half-life- the time necessary for one half of the unstable isotope to decay to a stable isotope - To find the age of a sample you need to know the parent to daughter ratio, the measured graph of half-life decay, and the number of half- lives.

14. 4. Dating with Carbon-14 - used to date recent events All living things contain carbon-14 When an organism dies the amount of carbon 14 gradually decreases to carbon 12 Knowing the ratio of carbon 14 to carbon 12, radiocarbon dates can be determined.

15. Radiometric Dating Activity

16. III. Sedimentary Rocks- formed from compacted and cemented sediments A. Layers of sedimentary rock often contain fossils and hold the clue to Earth’s geologic and biologic history B. Source of Sediments 1. Weathering breaks rocks down 2. Erosion involves weather and the removal of rock 3. Deposition is the dropping of sediments 4. Sediments are deposited according to size

17. C. How are Sedimentary Rocks formed 1. Sediment- small/fine pieces of rock 2.Sediments are moved by wind, water, ice, and gravity 3. Sediments eventually are dropped/deposited and form layers that get cemented together

18. 4. Final formation includes compaction and cementation a. Compaction- the squeezing out of water within and between layers due to the weight of material. b. Cementation occurs when the dissolved minerals seep into the spaces between sediments and binds them together

19. D. Classification of Sedimentary Rocks - based on formation 1.Clastic Sedimentary Rocks - formed from weathered bits of rocks and minerals - Grouped according to size of the sediments in the rock -example: conglomerate, sandstone, shale

20. 2. Chemical Sedimentary Rocks are formed when dissolved minerals precipitate from water solution -Examples include limestone, coquina,

21. Box of Rocks- sedimentary rocks Samples 6-10

22. E. A Brief History of Geology 1.Uniformitarianism - the same forces and processes we observe on the Earth now have been at work for a very long time. 2. Relative dating – gives us a sequence of events; allows us to see what layer is older or younger; no numbers

24. F. Relative Dating Key Principles 1.Law of superposition – in an unchanged layer of rocks, each layer is older than the one above it

25. 2. The principle of original horizontality- Layers of sedimentary rock begin in a horizontal position but get changed over time

26. 3. The principle of cross-cutting relationships a. faults or breaks in the layers are younger than the last layer it occurs in b. Intrusions- places where rock intrudes into another- are younger than the rock layer they are in

27. 4. Inclusions are rocks contained within other rocks a. Rocks containing inclusions are younger than the inclusions they contain.

28. 5. Rock is deposited, tilted, eroded, and then new layers are deposited on top of it a. The boundary between the layers is known as an unconformity.

29. G. Reading Rock Layers

31. See if you can do it!

32. IV. Metamorphic Rocks- form from existing rocks that undergo a change A. Formation of Metamorphic Rock 1. Contact metamorphism- metamorphic rocks that form from magma intruding into existing rock; the area of contact changes the existing rock - Low grade change; minor changes - Ex- marble; often forms when magma intrudes into limestone

34. 2. Regional Metamorphism – large scale change - Occurs over large areas during the mountain building process when rocks are exposed to extreme pressures and temperatures. - Large scale deformation, high grade metamorphism

36. B. Agents of Metamorphism- what causes metamorphic rocks to change 1. Heat -provides energy for chemical reactions→ reactions cause minerals to recrystallize or form new minerals -heat comes from magma and increase temperature deep within the earth 2. Pressure (Stress) - increase in depth of the earth causes an increase in pressure - increase pressure causes rock to flow not fracture- result is flat and elongated mineral grains

37. 3. Reactions to Solution - Hydrothermal solutions from magma cause recrystallization when original minerals are dissolved

38. C. Classification of Metamorphic Rocks- based on texture & composition 1.Foliated Metamorphic Rocks - Contact metamorphism compacts the mineral grains, increases the pressure and temperature, and causes the minerals to form in the same direction - Banded appearance from aligning of the mineral directions is known as foliation

40. 2. Nonfoliated Metamorphic Rocks - Metamorphic rock that does not have a banded appearance.

41. Box of rocks Metamorphic rocks Samples 11-15

42. V. Rock Cycle- rocks move in and out of the three rock families, they can spend any amount of time frame in one rock family and can take alternate paths to each family