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Rocks

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  1. Rocks Chapter 4 Earth Science Chapter 4

  2. Rock • Material that makes up solid parts of Earth • Can be made of • one or more minerals • Solid organic matter • Noncrystalline matter, such as glass Earth Science Chapter 4

  3. Rock-forming minerals • About twenty minerals that make up most rocks on Earth’s crust Earth Science Chapter 4

  4. Granite • Made of quartz, feldspar, hornblende, and mica • May also contain other minerals • Generally light-colored • High silica content Earth Science Chapter 4

  5. Basalt • Dark-colored • Low in silica • Very small mineral crystals Earth Science Chapter 4

  6. Grains • Small particles of minerals or other rocks that make up a rock • Grain size • Coarse, fine, or not visible • Grain shape • Rounded or jagged • Grain pattern • Nonbanded or banded Earth Science Chapter 4

  7. Texture • The look and feel of a rock’s surface Earth Science Chapter 4

  8. Igneous rock • From Latin term meaning “from fire” • Hardened magma or lava Earth Science Chapter 4

  9. Sedimentary rock • Compressed or cemented sediment • Sediment – rocks, minerals, and organic matter that has been broken into fragments Earth Science Chapter 4

  10. Metamorphic rock • Means “changed form” • Existing rock is altered by tremendous pressure, extreme heat, or chemical processes Earth Science Chapter 4

  11. Discuss • What three characteristics do geologists use to identify rocks? • What are the grains of a rock? • What are the three main groups of rocks? • Gneiss is a kind of rock that forms when heat and pressure inside Earth change granite. To what group of rocks does gneiss belong? Earth Science Chapter 4

  12. Igneous rock • Formed from lava or magma • Classified by origin, texture, and mineral composition Earth Science Chapter 4

  13. Origin • Extrusive rock • From lava • Basalt is most common • Intrusive rock • From magma • Granite is most common Earth Science Chapter 4

  14. Texture • Depends on size and shape of mineral crystals • Some igneous rocks cool so quickly that they lack crystal structure • Intrusive rocks have larger crystals • Cooled more slowly Earth Science Chapter 4

  15. Silica • Material formed form oxygen and silicon Earth Science Chapter 4

  16. Mineral composition • Lava low in silica forms dark-colored rocks • Basalt has feldspar and dark-colored minerals, but no quartz • Magma high in silica forms light-colored rocks • Granite rich in feldspar is speckled pink • Granite rich in hornblende and mica is light gray with dark specks • Quartz crystals add gray or smoky specks to granite Earth Science Chapter 4

  17. Building materials from igneous rocks • Granite is used for • Statues (over 3,500 years ago) • Fortresses (about 600 years ago) • Bridges, public buildings, and cobblestones (1800s and 1900s) • Curbstones, floors, and countertops (today) • Basalt is crushed and used in construction Earth Science Chapter 4

  18. Other uses of igneous rocks • Pumice’s rough surface makes it a good abrasive for cleaning and polishing. • Obsidian was used by ancient peoples to make sharp tools. Earth Science Chapter 4

  19. Discuss • How are igneous rocks classified? • Compare and contrast granite and basalt in terms of their origin and texture. Which is extrusive? Which is intrusive? • Would pumice be a good material to use to make a floor? Explain. Earth Science Chapter 4

  20. Sediment • Small, solid pieces • Come from rock, shells, bones, leaves, etc. Earth Science Chapter 4

  21. Sedimentary rock formation • Sediment is deposited by water and wind. • Most sedimentary rocks are formed by erosion, deposition, compaction, and cementation. Earth Science Chapter 4

  22. Erosion • Running water, wind, or ice loosen and carry away fragments of rock Earth Science Chapter 4

  23. Deposition • Sediment settles out of the water or wind carrying it • Sinks to the bottom of the water Earth Science Chapter 4

  24. Compaction • Sediments are pressed together by weight of layers above • Minerals dissolve in the water Earth Science Chapter 4

  25. Cementation • Dissolved minerals crystallize and glue particles together Earth Science Chapter 4

  26. Discuss • What is sediment? • In layers of sedimentary rock, where would you expect to find the oldest layers? Explain. • Place these steps in the formation of sedimentary rock in the proper sequence: compaction, erosion, cementation, deposition. Earth Science Chapter 4

  27. Major groups of sedimentary rocks • Clastic rocks • Organic rocks • Chemical rocks Earth Science Chapter 4

  28. Clastic Rocks • Formed when rock fragments are squeezed together • Shale • Clay particles in thin, flat layers • Sandstone • Forms from sand • Mostly quartz • Conglomorate • Rounded rock fragments • Breccia • Jagged rock fragments Earth Science Chapter 4

  29. Organic Rocks • Remains of plants and animals in thick layers • Coal • Remains of swamp plants (takes millions of years to form) • Limestone • Shells from coral, clams, and oysters (millions of years to form) Earth Science Chapter 4

  30. Chemical Rocks • When minerals dissolved in solution crystallize • Limestone • When dissolved calcite comes out of solution • Rock salt • When seas or lakes evaporate Earth Science Chapter 4

  31. Uses • Flint arrowheads • Hard, yet can be shaped • Formed when silica settles out of water • Sandstone and limestone building materials • Soft enough to be easily cut • Limestone used in making cement and steel Earth Science Chapter 4

  32. Discuss • What are the three main types of sedimentary rock? • What process causes deposits of rock salt to form? What type of sedimentary rock is rock salt? • The particles of sediment that make up shale are not usually well cemented. Would shale be a good choice of building material in a wet climate? Earth Science Chapter 4

  33. Metamorphic rock • Can be made from any other rock being changed by heat and/or pressure • May become smoother • Minerals in the rock may change into other minerals • Classified according to the arrangement of the grains that make up the rocks Earth Science Chapter 4

  34. Foliated rocks • Grains arranged in parallel layers or bands • May split apart along these bands Earth Science Chapter 4

  35. Nonfoliated rocks • Mineral grains arranged randomly Earth Science Chapter 4

  36. Uses • Marble • Limestone subjected to heat and pressure • Has fine, even grain • Can be cut thin or carved into shapes • Easy to polish • Flooring, statues, buildings • Slate • Foliated – splits easily into flat pieces • Flooring, roofing, sidewalks, chalkboards Earth Science Chapter 4

  37. Discuss • What does metamorphic mean? • How do geologists classify metamorphic rocks? • Describe foliated and nonfoliated rocks. • Which might be more useful for carving chess pieces, marble or slate? Earth Science Chapter 4

  38. Rock cycle • Series of processes on Earth’s surface and in the crust and mantle that slowly change rocks from one kind to another • Any of the three major types of rock can be changed into another of the three types • There are many possible pathways a rock can follow • See diagram on page 115 Earth Science Chapter 4

  39. Discuss • Website • Define the rock cycle in your own words. • What must happen in order for any rock in the rock cycle to become a sedimentary rock? Earth Science Chapter 4