EQ: How are rocks formed?

1. ls streak the EQ: How are rocks formed? Standard S6E5.c Classify rocks by their process of formation.

2. EQ: How Are Rocks Classified? • What three characteristics do scientists use to identify rocks? • What are the three groups into which geologists classify rocks? • What is a rock’s texture? • What do the three major groups of rock have in common? How are they different?

3. How geologists Classify Rocks • Rocks are made of minerals and a mixture of other materials • Some rocks are made of a single mineral • When studying a rock sample, geologists observe the rock’s texture, origin and mineral composition

4. A Rock’s Texture • A rock’s texture is the size, shape, and pattern of the rock’s grains Grain Size a. fine-grained (small-basalt) b. coarse-grained (large-granite) Grain Shape a. smooth and rounded (conglomerate) b. jagged (breccia) Grain Pattern a. foliated (gneiss) -lie in flat layers . vy, -wavy, swirling patterns b. nonfoliated (marble) c. looks like rows of multicolored beads d. occur randomly No Visible Grain a. have no apparent grains

5. Mineral Composition • By looking at a small sliver of a rock under a microscope, geologists can observe the size and shape of the crystals and identify the minerals the rock contains • Also, geologists can do tests to identify the physical properties of the minerals inside the rock. • mafic= dark-colored rocks (poor in silica) (basalt) • felsic = light-colored rocks (rich in silica) (granite)

6. Rock Origin Origin how and where the rock was formed 1. igneous rock = forms from the melting, cooling and hardening of molten rock a. extrusive= formed above the surface (lava) b. intrusive = formed below the surface (magma) 2. sedimentary rock = forms in layers from other rocks, plants, and animals through a process of weathering, erosion, deposition, compaction and cementation a. clastic rock b. organic rock c. chemical rock 3. metamorphic rock = formed when existing rock is changed by heat, pressure, or chemical reactions a. foliated rock b. nonfoliated rock

7. Compare and Contrast Rocks Compare – Rocks in each group make up the Earth’s crust and are composed of minerals and other materials Contrast – Rocks are different in the way they are formed

8. What characteristics are used to classify igneous rocks? Describe three (3) ways in which igneous rocks differ. What is the difference between extrusive and intrusive rocks? Give an example of each. Why are some igneous rocks dark and others light? How do igneous rocks form?

9. Origins of Igneous Rock • Igneous rocks are classified by their origin. • Igneous rocks are classified by the texture of the grains • Igneous rocks are classified by the mineral composition of the rock • Igneous rock forms when magma cools and hardens. • Three ways magma can form: • heat/rise in temperature • pressure released • rock changes composition

10. Composition and Texture of Igneous Rock • Igneous rocks differ from one another in what they are made of, how fast they are cooled and where the rocks form. • Composition – • Igneous rock that is rich in silicon and light-colored are called felsic rock. • Igneous rock that is poor in silicon and dark-colored are called mafic rock. • Texture – • Fine-grained (small) = cools quickly • Coarse-grained (large) =cools slowly

11. Origin of Formation • Igneous rock formations are located below and above Earth’s surface. • Intrusive igneous rock – Intrusive rock (granite) forms when magma hardens (beneath) Earth’s surface. • coarse-grained (large grains) • below Earth’s surface • ex. granite • Extrusive igneous rock – Extrusive rock (basalt) forms from lava that has erupted (onto) Earth’s surface. • fine-grained (small grains) • on the Earth's surface • ex. basalt

12. How do igneous rocks form? • Igneous rocks are classified according to their origin, texture, and mineral composition. • Igneous rocks form either from lava, above the earth’s surface or magma, below the earth’s surface. • They also differ in texture according to the size and shape of their mineral grains. (course-grained or fine-grained) • Igneous rocks differ in mineral composition depending on how much silica and other minerals are present. (felsic or mafic) • Dark igneous rocks form from magma or lava low in silica content (mafic). • Light igneous rocks form from magma high in silica content (felsic). • Light-colored rocks are less dense than the dark-colored rocks.

13. Uses of Igneous Rock • Most igneous rocks are hard, dense, and durable. • Ancient Native Americans used obsidian for making very sharp tools for cutting and scraping. • Granite is used as a building material such as decorative stonework, curbstones, and floors.. • Basalt is crushed to make gravel. • The rough surface of pumice makes a good abrasive for cleaning and polishing. • Perlite is often mixed with soil for starting vegetable seeds.

14. Quick Check 1. Which of the following are ways magma is formed? • by compaction and cooling • by melting and cooling • by changes in composition • by weathering and erosion

15. Quick Check • What kind of texture does igneous rock have when magma cools slowly? • coarse-grained • large-grained • fine-grained • medium-grained

16. Quick Check 3. What kind of texture does igneous rock have when magma cools rapidly? • coarse-grained • medium-grained • large-grained • fine-grained

17. Quick Check 4. What kind of rock is formed when magma intrudes into other rock? • extrusive igneous rock • sedimentary rock • intrusive igneous rock • organic sedimentary rock

18. Quick Check 5. What kind of rock is formed from lava that cools on Earth’s surface? a. organic sedimentary rock b. sedimentary rock c. intrusive igneous rock d. extrusive igneous rock

19. Describe the origin of sedimentary rock. Describe the three main categories of sedimentary rock. Describe three types of sedimentary structures. How is sedimentary rock formed?

20. Sedimentary rocks form from particles deposited by water and wind. After sediment has been deposited, the processes of compaction and cementation change the sediment into sedimentary rock. What is sedimentary rock?

21. Forming of Sedimentary Rock • Weathering- the breaking down of rock • Erosion – occurs when running water or wind loosen and carries away fragments of rock. • Deposition- the process in which sediment settles out of the water or wind carrying it. • Compaction- the process that presses sediment together. • Cementation- the process in which minerals crystallize and glue particles of sediment together.

22. Geologists classify sedimentary rocks according to the type of sediments that make up the rock. There are three major groups of sedimentary rocks: clastic rocks, organic rocks, and chemical rocks. Types of Sedimentary Rock

23. A clastic rock is a sedimentary rock that forms when rock particles are squeezed together. Examples of clastic rocks: Shale Sandstone Conglomerate Breccia Clastic Rocks

24. Shale forms from tiny particles of clay. Shale feels smooth, and splits easily into flat pieces Clastic Rock: Shale

25. Sandstone forms from the sand on beaches, on the ocean floor, in riverbeds, and in sand dunes. Sandstone is formed when small particles of sand are pressed and cemented together. . Clastic Rock: Sandstone

26. Conglomerate is a rock made up of large particles with rounded edges. Breccia is a rock made up of large fragments with sharp edges. Clastic Rock: Conglomerate and Breccia

27. Organic rock forms from the remains of plants and animals and are deposit in thick layers. The term “organic” refers to substances that were once part of living things. Three important organic rocks: Coal Limestone Chalk Organic Rocks

28. Coal forms from the remains of swamp plants buried in water. Over millions of years, they slowly change into coal. Organic Rock: Coal

29. The hard shell of living things produces limestone. Chalk forms from sediments made of skeletons of microscopic living things found in the ocean. Organic Rock: Limestone

30. Chemical rock forms when minerals that are dissolved in a solution crystallize. Chemical rocks can also form when mineral deposits left when seas or lakes evaporate. Examples: Rock salt gypsum Chemical Rocks

31. Sedimentary Rock Structures • The most important feature of sedimentary rock is stratification. • Stratification is the process in which sedimentary rocks are arranged in layers. • Strata differ from one another depending on the kind, size, and color of their sediment. • Ripple marks (1) are made by the motion of wind and water waves on lakes, oceans, rivers, and sand dunes. • Mud cracks (2) form when fine-grained sediments at the bottom of a shallow body of water are exposed to air and dry out. • Rain-drop (3) impressions can be preserved in fine-grained sediments, as small pits with raised rims.

32. Uses of Sedimentary Rocks • Sandstone and limestone are used as building materials. • The White House in Washington, D.C. is built of sandstone. • Limestone is also used to make cement.

33. Quick Check 1. Which process forms sediment? • weathering • cementation • compaction • deposition

34. Quick Check 2. What are strata? • mineral fragments • minerals crystallized out of solution • layers in sedimentary rock • fossils in sedimentary rock

35. Quick Check: Sedimentary Rock 3. What kind of sedimentary rock is made of fragments of rocks cemented together by a mineral? • organic • stratified • chemical • clastic

36. Quick Check 4. What kind of sedimentary rock is made from solutions of dissolved minerals in water? • organic • chemical • stratified • clastic

37. Quick Check 5. What kind of sedimentary rock is made from fossils? • organic • stratified • chemical • clastic

38. Quick Check 6. What is the process called in which sedimentary rocks are arranged in layers? • erosion • extrusion • weathering • stratification

39. How are metamorphic rocks formed? Describe two ways a rock can undergo metamorphism. Describe the difference between foliated and nonfoliated metamorphic rock. How is metamorphic rock formed?

40. How Do Metamorphic Rocks Form? • Metamorphic rock is formed when existing rock is changed by heat, pressure, or chemical reactions. • Heat and pressure deep beneath Earth’ssurface can change any rock into metamorphic rock. • Metamorphic rocks are classified by the arrangement of their mineral grains.

41. Textures of Metamorphic Rock • The two types of metamorphic rocks are called foliated rock and non-foliated rock. • Foliated rock is when the grains are parallel or arranged in planes or bands. • gneiss (from granite) • Slate (from shale) • Non-foliated rock refers to where the grains are arranged randomly. • Marble (from limestone) • Quartzite (from sandstone)

42. Gneiss Schist Foliated Metamorphic Rock

43. Quartzite Marble Nonfoliated Metamorphic Rocks

44. Composition of Metamorphic Rock • Metamorphism occurs when temperature and pressure inside the Earth’s crust change. • Minerals that were present in the rock when it formed may not be stable in the new temperature and pressure conditions. • The original minerals change into minerals that are more stable in these new environment. • Some metamorphic minerals form only at certain temperatures and pressures. • Common metamorphic rock: slate, schist, marble, and gneiss.

45. Metamorphic Rocks • The texture or mineral composition of a rock can change when its surroundings change. • If the temperature or pressure of the new environment is different from the one in which the rock formed, the rock will undergo metamorphism. • Two ways that rock can undergo metamorphism are by contact metamorphism and regional metamorphism. • Contact metamorphism happens near bodies of magma. • Regional metamorphism occurs within Earth’s crust when pressure builds up in rock very deep below other rock formations

46. Metamorphic Rock Structures • Metamorphic rock has features that tell you about its history. • In metamorphic rocks, these features are caused by deformation. • Deformation is a change in the shape of a rock caused by a force placed on it. • These forces may cause a rock to be squeezed or stretched. • Folds or bends in metamorphic rock are structures that indicate that a rock has been deformed.

47. Uses of Metamorphic Rock • Marble and slate are the two most useful metamorphic rocks. • Marble can be cut into thin slabs and easily polished (Taj Mahal). • Slate , because it is foliated, splits easily into flat pieces. • Slate is used for flooring, roofing, outdoor walkways, or chalkboards. • Marble and Slate both come in a variety of colors.

48. Summary… • There are 3 major rock groups: igneous rocks sedimentary rocks and metamorphic rocks. • Igneous rocks form when molten rock cools and hardens from magma or lava. • Sedimentary rocks form from particles deposited, pressed, and cemented together by water and wind. • Metamorphic rocks form from heat and pressure, or a chemical reaction. • Forces inside Earth and at the surface produce a rock cycle that builds, destroys, and changes the rocks in the crust.

49. Quick Check 1. How does metamorphic rock form? a. by intense heat and pressure b. erosion, deposition, compaction, cementation c. melting into lava or magma, then cooling into a new rock d. by pressing together and then cementation

50. Quick Check 2. Molten rock beneath Earth’s surface is called a. lava. b. magma. c. sedimentary rock. d. igneous rock.