Rocks

 Sedimentary rock: formed by pieces of rock carried by water, wind, or ice  Warm-Up:  What was your favorite food you ate on Thanksgiving?  How are rocks and minerals related?  What are some everyday uses for rocks?

 Metamorphic rock: formed by high heat, high pressure, or both  Warm-Up:  How could sedimentary or igneous rock change to metamorphic?  How could igneous or metamorphic change to sedimentary?

 Shield volcanoes: broad, gently sloping cones  Warm-Up:  List the 3 types of rocks and explain how each forms

 The Earth’s surface is constantly changing due to the theory of plate tectonics  Earth’s rocks are classified into three categories  Igneous rocks: formed by the cooling and crystallization of magma  Make up 95% of the earth’s crust  Examples: Basalt, granite

 Sedimentary rocks: formed from pieces of other rocks carried by water, wind, or ice  Most common on the earth’s surface  Examples: sandstone, shale, limestone  Metamorphic rocks: formed from older rocks that are changed by high temperature, high pressure or both  Examples: marble, slate

 Some Igneous rocks form at the earth’s surface  Igneous rocks that form at the earth’s surface are called extrusive  Magma can differ in the amount of silicon it contains  What does silicon determine?  Melting temperature

 Higher amounts of silicon = thick, more viscous magma  What does viscous mean?  Gooey, sticky  Lower amounts of silicon = thinner, faster flowing magma  Spilled milkshake vs. spilled milk  Basaltic magma- important low-silicon, fast- flowing magma

 Temperature also affects magmas ability to flow  Hotter magma flows better than cooler magma  Lava – magma that flows onto the surface of the earth  Lava most commonly comes out of fractures and cracks in the earth’s surface called fissures  Can also come out of a central vent or volcano

 Lava can come up through cracks underwater or on land  Some igneous rocks form below the earth’s surface  These rocks are called intrusive  Large intrusive rocks are plutons  Concept check:  Why is it incorrect to say that igneous rocks may form from the intrusion of lava?  How could you correct the statement?

 Most common rock on earth’s surface  Covers 2/3 of the Earth’s surface

 Volcanism constantly makes new rock and weathering is the opposite process; it breaks down rock  Two kinds of weathering  Mechanical– physically breaks rocks into smaller pieces  chemical- chemical reactions that involve water and decompose rock into smaller pieces Erosion- process that removes weathered rock particles and transports them by wind, water, or ice

 When transportation stops, deposition and sedimentation begin  Deposition – particle being transported stops and is deposited  Larger grains are deposited first  Grains end up sorted by size

 Sedimentation – sediment particles are deposited one layer at a time  As sedimentation builds up it starts changing into sedimentary rock  Occurs in two ways:  compaction- layers are pressed together and water is squeezed out  cementation- chemicals in the water fill the pores and act like a glue to hold the grains together

 Clastic Sediments – sediments composed of small fragments of other rocks  Three most abundant: shale, sandstone, conglomerate  Limestone and evaporitesare also sedimentary rocks  Sedimentary rock contain fossils

 Why would sedimentary rock contain fossils?  Fossils are important for information about the past  Fossil Fuels-  oil- Sediment is buried and heated over a long period of time  Natural gas – higher temperature  coal- plants that do not completely decay

 All three types of rock can undergo change and becomes metamorphic  Example of metamorphism:  Potter’s clay  NO MELTING OCCURS!  Recrystallization – minerals in a rock change because the rock is exposed to high temperature and pressure  Mechanical deformation- rock is subjected to physical stress deep in earth’s crust

 Two Kinds of Metamorphism  contact- occurs when a body of rock is intruded by magma  causes increased grain size due to recrystallization  Near contact = low water content, larger crystal size  regional- rocks change when subjected to physical stress and heat over a large region  Found a lot in mountains  Heat and pressure can produce beautiful gems

 Foliated Metamorphic Rock – has a layeredappearance  Examples: slate, schist, gneiss  Nonfoliated metamorphic rocks have a smoother appearance  Foliation only develops if the pressure is high enough, if not, we get nonfoliated rocks  Examples: marble, quartzite