The Rock Cycle Igneous Rocks Metamorphic Rocks Sedimentary Rocks
WHAT IS A ROCK? Rocks are classified as mixtures. They are mixtures of: Minerals Mineraloids Glass Organic matter
THE ROCK CYCLE The rock cycle shows how one rock changes into another. The following are processes that change rocks. Weathering Erosion Compaction Heat & pressure Cementation Melting Cooling
THE ROCK CYCLE
IGNEOUS ROCKS (Latin ignis meaning “fire”) Most abundant type of rock on Earth Magma and lava cool to form igneous rocks Magma = melted rock below the Earths surface Lava = melted rock on the surface of the Earth You classify igneous rock by where it formed (intrusive or extrusive) and by the types of minerals in them. An igneous rock can be either basaltic, granitic or andesitic
INTRUSIVE IGNEOUS ROCKS Magma is insulated deep inside the Earth so it cools slowly. When magma cools slowly the atoms have time to arrange into large crystals called mineral grains Example of intrusive rocks: Gabbro Diorite
EXTRUSIVE IGNEOUS ROCKS Lava is on the Earth’s surface so it cools fast. The quick rate of cooling keeps large mineral grains from forming. Often the individual grains are too small to be seen without magnification. Example of extrusive rocks: Obsidian – smooth glass Pumice & scoria – glass with holes or pockets that formed as air & other gasses escaped the cooling rock
BASALTIC IGNEOUS ROCKS Form from basaltic magma or lava Dense,heavy, dark colored rocks Rich in iron and magnesium Flow from volcanoes in Hawaii Does this help explain the black sand beaches of Hawaii?
GRANITIC IGNEOUS ROCKS Granitic magma and lava are thick, stiff & contain a lot of silicon and oxygen Light-colored rock Lower density than basaltic rock Granitic magma builds up a lot of pressure that is released during violent volcanic eruptions
ANDESITIC IGNEOUS ROCKS Mineral composition between those of basaltic and granitic rocks Many volcanoes in the Pacific ocean are andesitic
METAMORPHIC ROCK Rocks that have changed due to temperature & pressure and/or changes in composition Can be formed from changes to igneous, sedimentary or other metamorphic rocks. Ex: Grains in granite get flattened and line up when pressure is applied to them forming gneiss Ex: Grains in shale are arranged into layers when heat and pressure is applied forming slate
SEDIMENTARY ROCKS Form when sediments become pressed or cemented together or when sediments precipitate out of solution. Erosion moves sediments to a new location Layer upon layer of sediment build up Pressure from the upper layer pushes down If sediment is small they stick together to form solid rock If sediment is large the pieces get cemented together by minerals dissolved in water
CLASSIFICATION OF SEDIMENTARY ROCKS Clastic – made up of broken fragments of rock, plants or animals Conglomerate (round sediments) & Breccia (sharp angled sediments) form from large sediments Chemical – form from minerals precipitated out of solution or left behind from evaporation. Ex: rock salt Organic – rock form from once living things Ex: fossil-rich limestone (writing with chalk is smearing calcite shells of once living animals)
Chapter 4 QUIZ Where are Igneous rocks formed? How are Metamorphic rocks formed? How are sedimentary rocks formed? What is the difference between the formation of intrusive and extrusive Igneous rocks?
Answers Please!
Chapter 4 QUIZ How are Igneous rocks formed? In magma or lava How are Metamorphic rocks formed? A change takes place How are sedimentary rocks formed? Build up of sediments that get compressed What is the difference between the formation of intrusive and extrusive Igneous rocks? Intrusive - formed inside volcano in magma Extrusive - formed outside volcano in lava