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ROCKS, ROCKS, AND MORE ROCKS! Chapters 5 and 6 (Glencoe Earth Science) What is a rock? A rock is a hard substance made of one or more minerals There are 3 types of rocks: Igneous Sedimentary Metamorphic What’s an Igneous Rock? Formed by crystallization of magma Igneous comes from the latin word for fire These rocks are associated with fiery lava flows Lava is magma that flows on the Earth’s surface Types of Igneous Rocks Extrusive Formed from lava on Earth’s surface that cooled quickly Known as volcanic rock Fine-grained Intrusive Formed inside the Earth Magma rises up into pre-existing rocks and hardens Coarse-grained Called “Plutonic” rocks after Pluto, the god of the Underworld These rocks commonly produce landforms Granite is most common Igneous Rocks Which is the intrusive rock? Which is the extrusive rock? What About Igneous Rocks? Useful as building materials Interlocking grainy texture provides strength Resistant to weathering Granite is especially durable Used for columns, tiles and countertops, etc. Valuable ore deposits are often associated with igneous rocks It’s Sedimentary, Watson! What’s a sedimentary rock? A rock formed from sediments Sediments are pieces of material that have been carried/deposited by wind, water, etc. Sedimentary rocks form when these pieces are cemented together How do Sedimentary Rocks Form? Weathering Processes that break rock into smaller pieces Chemical-minerals in rock are dissolved or chemically changed Physical-minerals are unchanged; rock fragments break off Erosion Movement Caused of materials from one location to another by wind, moving water, gravity, glaciers (ice) Eroded materials almost always moved downhill Sediments, Classified Clastic Rock Refers to fragments of rock and minerals created by weathering and erosion Clastic comes from the Greek word for “broken” Classified by particle size Deposition Occurs when sediments are laid down on the ground or sink to the bottom of a body of water When wind/water slows down, largest particles settle out first, etc. Smallest particles settle last. Sediments moved by glaciers and landslides are not sorted. Burial Most sediments are deposited in basins (depressions) As more sediments are deposited, the layers on the bottom are exposed to more heat and pressure. Causes lithification Physical and chemical processes that turn sediment into sedimentary rock Process of Lithification 1-Compaction Weight of sediments forces them closer together Water is squeezed out of mud Sand resists compaction because of grain-to-grain contact Process of Lithification 2-Cementation Temperatures increase Buried sediments can be chemically changed Mineral growth cements sediments together into solid rock Two types of cementation A new mineral grows between grains OR The same mineral grows between or over grains Features of Sedimentary Rock Horizontal layering (bedding) Graded bedding: particle size becomes more coarse/heavy toward bottom layers Cross-bedding: formed as inclined layers of sediment move forward across a horizontal surface Fossils Evidence of once-living organisms Types of Sedimentary Rock Clastic Rock Most common; formed from deposits of loose sediments 1/3 or more is pebble-called conglomerate Not If as common as rock w/ smaller pieces made with sandy grains-called sandstones Very common Particles smaller than sand-called shale Types of Sedimentary Rock Chemical Rocks Formed when water evaporates leaving minerals behind Ex: Rock salt, some limestone Stalactites, stalagmites Organic Sedimentary Rocks Formed Ex: coal from remains of a once-living thing Why are Sedimentary Rocks Important? Energy Resources Coal, Oil, Natural gas are found in sedimentary rock Many metals are mined from sedimentary rocks Used in making cement (limestone) Used in making blocks for walls (sandstone, limestone) Metamorphic Rock Changing one type of rock into another as a result of extreme heat, pressure, and/or chemical reactions Can be formed from any of the three types of rock The ‘new’ rocks have different properties than the rock did before the ‘morph’ The Rock Cycle Continuous changing and remaking of rocks Rocks are constantly being recycled from one type to another Example of the Path of a Rock Through the Rock Cycle Granite (igneous rock) Wind/rain erodes exposed rock, bits flake off, carried to bottom of stream carried to river, along with other sediments carried to sea, deposited Deposits build up form sandstone (sedimentary rock) Sediments continue to be buried and are under more pressure/higher temps pressed together even more form quartzite (metamorphic rock)AND THE CYCLE CONTINUES…
