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Rocks: Mineral Mixtures

Rocks: Mineral Mixtures. Chapter 4. The Rock cycle. Section 1. Introduction. Rock: a naturally occurring solid mixture of one or more minerals and organic matter Rock cycle: the continual process by which new rock forms from old rock material. Processes that Shape the Earth.

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Rocks: Mineral Mixtures

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  1. Rocks: Mineral Mixtures Chapter 4

  2. The Rock cycle Section 1

  3. Introduction • Rock: a naturally occurring solid mixture of one or more minerals and organic matter • Rock cycle: the continual process by which new rock forms from old rock material

  4. Processes that Shape the Earth • Weathering, Erosion, and Deposition • Weathering: the process in which water, wind, ice, and heat break down rock • Erosion: the process by which sediment is removed from its source • Deposition: the process in which sediment moved by erosion is dropped and comes to rest • Deposited in bodies of water and other low-lying areas

  5. Processes that Shape the Earth • Heat and Pressure • Sedimentary rock made of sediment can also form when buried sediment is squeezed by the weight of overlying layers of sediment • If temperature and pressure are high enough, the rock can change into metamorphic rock • The melting of rocks creates the magma that eventually cools to form igneous rock

  6. Processes that Shape the Earth • How the Cycle Continues • Uplift: movement within the Earth that causes rocks inside the Earth to be moved to the Earth’s surface • When uplifted rock reaches the Earth’s surface, weathering, erosion, and deposition begin

  7. Weathering > Erosion > Deposition > Compaction and Cementation > Metamorphism > Melting > Cooling > Solidification > Weathering SEDIMENT IGNEOUS ROCK SEDIMENTARY ROCK MAGMA! METAMORPHIC ROCK

  8. Sedimentary Rock • Grains of sand and other sediment are eroded from hills and mountains and wash down a river to the ocean. Over time, the sediment forms thick layers on the ocean floor. Eventually, the grains of sediment are compacted and cemented together to form sedimentary rock.

  9. Metamorphic Rock • When large pieces of the Earth’s crust collide, some of the rock is forced downward. At great depths, intense heat and pressure heat and squeeze the sedimentary rock to change it into metamorphic rock.

  10. Magma • The hot liquid that forms when rock partially or completely melts is called magma. Where the metamorphic rock comes into contact with magma, the rock tends to melt. The material that began as a collection of sand grains now becomes part of the magma.

  11. Igneous Rock • Magma is usually less dense than the surrounding rock, so magma tends to rise to higher levels of the Earth’s crust. Once there, the magma cools and solidifies to become igneous rock.

  12. Sediment • Uplift and erosion expose the igneous rock at the Earth’s surface. The igneous rock then weathers and wears away into grans of sand and clay. These grains of sediment are then transported and deposited elsewhere, and the cycle begins again.

  13. Round and Round it Goes • Each rock type can change into one of the three types of rock • As one rock is changed into another type, several variables, including time, heat, pressure, weathering, and erosion, may alter a rock’s identity

  14. Rock Classification • Scientists divide all rock into three main classes based on how the rock is formed • Igneous • Sedimentary • Metamorphic • Can be divided further • Divisions based on differences in the way rocks form • Two important criteria for divisions—composition and texture

  15. Rock Classification • Composition • The chemical makeup of a rock; describes either the minerals or other materials in the rock

  16. Rock Classification • Texture • The size, shape, and positions of the grains that make up a rock • Sedimentary rock: fine-grained, medium-grained, or coarse-grained texture • Igneous rock: fine-grained or coarse-grained texture • Metamorphic rock: fine-grained or coarse-grained texture

  17. Rock Classification • Texture • Can provide clues as to how and where the rock formed • Can reveal the process that formed it Fine-grained Medium-grained Coarse-grained

  18. Igneous rock Section 2

  19. Origins of Igneous Rock • Forms when magma cools and solidifies • Three ways magma can form: • When rock is heated • When pressure is released • When rock changes composition

  20. Composition and Texture of Igneous Rock • Light-colored rocks are less dense than the dark-colored rocks • Felsic rocks: light-colored rocks rich in elements such as aluminum, potassium, silicon, and sodium • Mafic rocks: dark-colored rocks rich in calcium, iron, and magnesium, and poor in silicon

  21. Composition and Texture of Igneous Rock • The more time the crystals have to grow, the larger the crystals are and the coarser the texture of the resulting igneous rock is

  22. Igneous Rock Formations • Located above and below the surface of the Earth • Intrusive Igneous Rock • When magma pushes into surrounding rock below the Earth’s surface and cools • Has a course-grained texture • Cools very slowly

  23. Igneous Rock Formations • Masses are named for their size and shape • Plutons: large, irregular-shaped intrusive bodies • Batholiths: largest of all igneous intrusions • Stocks: intrusive bodies that are exposed over smaller areas than batholiths • Dikes: sheet-like intrusions that cut across previous rock units • Sills: sheet-like intrusions that are oriented parallel to previous rock units

  24. Igneous Rock Formations • Extrusive Igneous Rock • Igneous rock that forms from magma that erupts onto the Earth’s surface • Common around volcanoes • Cools quickly • Very small crystals or no crystals

  25. Sedimentary Rock Section 3

  26. Origins of Sedimentary Rock • Sandstone: sand grains that are compressed and then cemented together over time • Sediment: rock and mineral fragments • Deposited in layers • Dissolved minerals separate from water that passes through the sediment to form a natural cement that binds the rock and mineral fragments together in sedimentary rock • Forms at or near Earth’s surface • Forms without heat or pressure

  27. Composition of Sedimentary Rock • Classified by the way it forms • Clastic sedimentary rock: forms when rock or mineral fragments are cemented together • Chemical sedimentary rock: forms when minerals crystallize out of a solution to become rock • Organic sedimentary rock: forms from the remains of once-living plants and animals

  28. Composition of Sedimentary Rock • Clastic Sedimentary Rock • Made of fragments of rocks cemented together by a mineral such as calcite or quartz • Have coarse-grained, medium-grained, or fine-grained textures

  29. Composition of Sedimentary Rock • Chemical Sedimentary Rock • Forms from solutions of dissolved minerals and water • Some of this dissolved material eventually crystallizes and forms the minerals that make up chemical sedimentary rock

  30. Composition of Sedimentary Rock • Organic Sedimentary Rock • Forms from the fossils of animals or plants • Fossiliferous limestone: animal remains that eventually become cemented together • Made from: • Coral • Clams • Oysters • Coal: forms underground when partially decomposed plant material is buried beneath sediment and is changed into coal by increasing heat and pressure over millions of years

  31. Sedimentary Rock Structures • Stratification: the process in which sedimentary rocks are arranged in layers • Sedimentary rocks sometimes record the motion of wind and water waves • Ripple marks • Mud cracks • Indicate the location of an ancient lake, stream, or ocean shoreline • Even rain drop impressions can be preserved

  32. Sedimentary Rock Impressions

  33. Metamorphic Rock Section 4

  34. Origins of Metamorphic Rock • Rocks in which the structure, texture, or composition of the rock have changed • Metamorphosis= changed shape • Most metamorphosis takes place from 50°C to 1,000°C • Some take place at more than 1,000°C • Most metamorphosis takes place at depths greater than 2 km • This pressure can cause the mineral grains in rock to align themselves in certain directions

  35. Origins of Metamorphic Rock • Contact Metamorphism • Occurs near igneous intrusions • Occurs because of magma heating the rock around it as it moves • Regional Metamorphism • When pressure builds up in rock that is buried deep below other rock formations or when large pieces of Earth’s crust collide with each other • Occurs over thousands of cubic kilometers • Rocks that have undergone this are found beneath most continental rock formations

  36. Origins of Metamorphic Rock

  37. Composition of Metamorphic Rock • Index minerals: metamorphic minerals that form only at certain temperatures and pressures • Examples: • Biotite • Mica • Chlorite • Garnet • Kyanite • Muscovite mica • Sillimanite • Staurolite

  38. Textures of Metamorphic Rock • All metamorphic rock has one of two textures—foliated or nonfoliated

  39. Textures of Metamorphic Rock • Foliated Metamorphic Rock • Foliated: the texture of metamorphic rock in which the mineral grains are arranged in planes or bands • Slate: when shale is exposed to slight heat and pressure, the clay minerals change into mica minerals

  40. Textures of Metamorphic Rock • Nonfoliated Metamorphic Rock • Nonfoliated: the texture of metamorphic rock in which the mineral grains are not arranged in planes or bands • Commonly made of one or only a few minerals • Recrystallization: the crystals of these minerals may change in size or the mineral may change in composition

  41. Metamorphic Rock Structures • Deformation: 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 • Bends

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