Rocks

1. Rocks and the Rock Cycle

2. Grand Canyon Facts What Civil War veteran first ran the Colorado River? How deep, wide, and long is the Grand Canyon?

3. Grand Canyon Facts What type of rock forms the layers in the canyon? What might these symbols mean?

4. Glen Canyon Dam Facts What type of rock is this? Why was this spot chosen for the dam site? What does the dam provide for the Southwest?

5. Rocks and the Science of Geology Elements Minerals Rocks Rock - a mixture of one or more minerals Geology - the study of the earth and its processes What can we learn from studying the clues in rocks? Color Texture Minerals Fossils Shape What processes were at work in the past? What processes are at work now? What was this area like in the past? What are our effects on the environment, and vice versa? By studying geology, we better understand our world.

6. Igneous Rocks • Granite is a very common rock here in New England, and is an example of an igneous rock. • Common minerals in granite: • Quartz • Feldspar • Mica • Hornblende

7. Igneous Rocks • Igneous Rock: rock that forms when molten material cools • As molten material (magma or lava) cools, it becomes solid (freezes). • Different minerals form as the magma cools. • The minerals that form depend on the elements that are present in the magma. • Molten material can cool slowly or quickly. So what?

8. Formed when magma cools below the surface Magma cools very slowly Mineral crystals have time to grow Large, visible mineral crystals (Coarse-grained texture) Formed when lava erupts and cools at the Earth’s surface Lava cools very fast Little or no time for crystals to grow Tiny crystals too small to see (fine-grained texture) GRANITE RHYOLITE Types of Igneous Rocks INTRUSIVE: EXTRUSIVE:

9. Classifying Igneous Rocks

10. Typical Igneous Rocks Granite • mostly quartz and feldspar • light-colored • magma cools slowly • coarse-grained • most abundant igneous rock on land • forms most of the continental crust

11. Typical Igneous Rocks Basalt • Dark, iron-rich minerals (olivine, pyroxene) • Contains no quartz • Dark-colored • Fine-grained • Forms the Earth’s ocean crust • Forms the lunar maria • Most commonly seen as lava flows

12. Typical Igneous Rocks Diorite • Little or no quartz • Light and dark minerals • intermediate Gabbro • Dark, iron-rich minerals (olivine, pyroxene) • Dark-colored • Common in New England

13. Typical Igneous Rocks Andesite • Same minerals, same general color as diorite • Commonly formed from thick lavas in volcanic eruptions • Named for? Rhyolite • Same general light color as granite • Rare, fine-grained rock • Very thick lava

14. Typical Igneous Rocks Scoria and Pumice • Cool and harden into rock while gases are escaping from the lava • Full of holes, like “rocky sponges” • Pumice is light, scoria is dark How do the holes affect the densities of these rocks? Based on their colors, these rocks are they most similar to? scoria = basalt and gabbro pumice = rhyolite and granite

15. A Unique Kind of Igneous Rock Obsidian • Natural volcanic glass • Forms when thick, rhyolitic lava cools rapidly • Lava cools so fast that crystals don’t have time to form at all • Natural and manmade glass are “supercooled liquids” (no crystal structure) Native Americans often traveled great distances to find sources of obsidian. Why was obsidian such a valuable substance to native cultures?

16. Classifying Igneous Rocks

17. Review of Igneous Rocks If you can answer these questions, you understand the basics! 1. What geologic processes are at work which explain and describe the formation of the Grand Canyon? 2. What is the difference between a mineral and a rock? 3. What are the common minerals in granite? Why is granite so resistant to weathering? 4. What is meant by the terms intrusive and extrusive? Compare and contrast. 5. What can a geologist tell from the overall color of an igneous rock? 6. What are some of the differences between granite and basalt, the two most common igneous rocks? 7. Why do scoria and pumice have the textures that they do? 8. How is the way obsidian forms related to its special properties? 9. Can you name, describe, recognize, and classify the main examples of igneous rocks?

18. Metamorphic Rocks • Minerals in igneous rocks often do not remain unchanged over millions of years • Metamorphic: meta “change” morph “form” • Metamorphic rocks are rocks that have been changed by heat and/or pressure • What happens to the minerals? • change shape • change size • atoms recombine into new, different minerals

19. Metamorphic Rocks • For example, granite (A) can be exposed to great pressure deep underground. • Rocks can also be exposed to great heat (without melting). • Rocks are “cooked” under pressure, forcing the minerals in the rock to change into different forms. • In this example, granite becomes granite gneiss (B), which is a metamorphic rock. • How is the rock now different?

20. Classifying Metamorphic Rocks • Based on what happens to the minerals, metamorphicrocks fall into two groups: • Foliated • Nonfoliated • In foliated rocks, the minerals flatten and line up as they are undergoing changes. • In nonfoliated rocks, the minerals change, combine, and rearrange, but don’t form visible bands or layers. • Foliated metamorphic rocks can be easily separated into layers, but nonfoliated rocks instead fracture into pieces of random size and shape.

21. Foliated Metamorphic Rocks Gneiss • Typically forms when pressure is applied to granite • Forms deep beneath the Earth’s surface • Minerals flatten and line up in alternating light and dark bands (foliation) Schist • Typically forms due to heat and pressure • Mineral grains grow larger or new minerals form • Flat, platy mica crystals are seen

22. Different metamorphic rocks are also produced as change continues to occur. Rocks go through stages as more heat and pressure are applied. Over millions of years… Mud becomes Shale becomes Slate becomes Schist becomes Gneiss Metamorphic Means Change

23. Nonfoliated rocks like marble are equally weak in all directions and can be carved in any direction. Marble is softer than the limestone from which it formed, because the minerals have been changed by heat and pressure. Foliated rocks like slate often cleave apart along the foliation, and have different uses. Foliated vs. Nonfoliated

24. Nonfoliated rocks like marble are equally weak in all directions and can be carved in any direction. Marble is softer than the limestone from which it formed, because the minerals have been changed by heat and pressure. Foliated rocks like slate often cleave apart along the foliation, and have different uses. Foliated vs. Nonfoliated

25. Metamorphic Rocks Review If you can answer these questions, you understand the basics! 1. What is the definition of a “metamorphic rock?” 2. What happens to the minerals making up the rock to be considered “metamorphic?” 3. How is the texture of gneiss different from that of granite? 4. What is meant by the terms foliated and nonfoliated? Compare and contrast. 5. What are some of the differences between gneiss and schist, which are two common foliated metamorphic rocks? 7. Describe how a sediment like mud can eventually become gneiss over millions of years. 8. Can you relate the properties of foliated and nonfoliated metamorphics to their uses in our society? Give specific examples.

26. Sedimentary Rocks • Sedimentary rocks, like those that form the layered rocks in the Grand Canyon, form from sediments. • On the continents, most of the rocks below the surface are igneous rocks, but most of the rocks exposed at the Earth’s surface are sedimentary rocks. • To understand how these rocks form, we have to first understand how sediments are created. • Two main processes are constantly at work changing the Earth’s surface over time: • Weathering • Erosion • But what’s the difference?

27. What is Weathering? • Weathering is the process of breaking up rocks or other solid materials into smaller pieces called sediments. • Mechanical weathering means breaking up the rocks by physical processes: • Freezing and thawing • Landslides • Wind and wave action • and even just rain! • all work to physically break up rocks over time • Chemical weathering can happen because minerals can undergo chemical reactions when exposed to the Earth’s environment: • For example, oxygen and acid rain • Chemical reactions in the rocks can alter minerals into weaker forms that are more easily worn away. • What kind of weathering is shown here?

28. Some Examples of Weathering

29. What is Erosion? • Erosion is the process of transporting sediments to new locations because of forces at work on the Earth’s surface. • This process is often confused with weathering (although weathering and erosion often work together). • The transportation of sediments is due to “agents” of erosion: • Wind • Water • Ice • Gravity • Erosion is occurring wherever these “agents” are at work. • Sediments are transported to new locations and deposited. If conditions are right, sedimentary rocks can form over time.