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Rocks & The Rock Cycle Unit D, Chapter 2 Introduction Questions 1. 2. 3. 4. 5. 6. 7. How can rocks change? What will cause rocks to change? How long will it takes rocks to change? What will the rocks change/turn into? Where do these changes occur? What is a cycle? What is the rock cycle? Igneous Rocks UD, C2, Section 1, pD40-45 Minerals • Rocks divided into 3 types – how they formed – Igneous – Sedimentary – Metamorphic • Rocks build landforms – Mountains – Volcanoes, etc. • Minerals build rocks Minerals • Minerals: solid substance with a definite chemical composition and physical structure – Form as crystals • Solids with regular geometric shape – Shows how atoms are arranged inside of it – 4000 different minerals (12 common) Minerals • Properties: (characteristics) – Hardness • Diamond – Hardest – Can scratch other substances • Talc – Softest – Fingernail can scratch it – Color – Crystal shape – Color of the streak when rubbed on tile – Density (mass ÷ volume) Formation of Igneous Rocks • Magma: melted rock inside the Earth – Heat and pressure in mantle melts rock • Lava: melted rock that reaches Earth’s surface Formation of Igneous Rocks • Igneous rock: forms when magma is pushed up from the mantle into the cool crust or onto the surface and hardens into rock – Crystallization: another name for hardening into rock Formation of Igneous Rocks • Intrusive: – Magma hardens under the surface – Cools slowly (millions of years) forming large crystals – Examples: Diorite, Granite, Gabbro • Landforms: – Shiprock, New Mexico • Magma cooled underground “pluton” • Weathering & erosion wears away softer rock around it • Exposes “batholith” Formation of Igneous Rocks • Extrusive: – Lava hardens on the surface – Cools quickly forming small/no crystals – Examples: Rhyolite, Andesite, Basalt, • Obsidian – glassy rock without crystals • Pumice – full of small holes, can float Uses of Igneous Rocks • Igneous rocks some of most common on Earth – Granite used as a building material • Looks nice, resists weathering – Obsidian used for tools, jewelry, and mirrors • Breaks with sharp edges, looks nice, glassy surface – Pumice used as scouring substance in soaps/cleaners • Can be pounded into powder – Igneous rocks are the source of many ores • Chromium, platinum, diamond, nickel, copper – Ore: useful minerals/mixtures or minerals that are mined Sedimentary Rocks UD, C2, Section 2 pD48-53 Formation of Sedimentary Rocks • Mostly found on surface (75%)(5% all crust) • Weathering: process of breaking rock into smaller pieces – Natural processes: • • • • Flowing water Moving ice Freezing & thawing (contraction & expansion) Growth of plants • Erosion: movement of sediment to new place Formation of Sedimentary Rocks • Deposition: dropping of sediment – Wind or water when it slows down • Slower means less kinetic energy to carry sediment – Ice when it melts • Sedimentation: build up of sediment layers over millions of years – Weight of layers compact (packs down) sediments • Cementation: glues packed particles together Formation of Sedimentary Rocks • Two main groups of sedimentary rocks – Clastic rocks: made of sediments that were weathered, transported, and deposited in layers – Chemical rocks: formed from minerals that were dissolved in water, came out of solution, and deposited Clastic Rocks • Clastic rocks classified by the size of sediments – Fine particles: Shale • Most common sedimentary rock • Often contain fossil imprints – Medium particles: Sandstone • Most sandstone contains the mineral: Quartz – Coarse, pebble-sized particles: • Smooth edges: Conglomerate – Transported long distances to smooth edges • Sharp edges: Breccia – Transported short distance, didn’t have time to round edges Chemical Rocks • Chemical weathering – Rocks breaks down into chemicals that dissolve • Like sugar dissolving in tea/coffee • Chemical rocks form in two ways – Evaporation leaves sedimentary rocks behind • Layer of salt at the bottom of dried-up lake – Animal shells or skeletons can also form rocks • Coral take chemicals out of water – make limestone reefs • Shells pile up, compacted, cemented – form Limestone – Limestone far from coast – clue to where ancient seas were Uses of Chemical Rocks • Sedimentary rocks make building materials – – – – – – Bricks, tile, pottery, china from Shale & Mudstone Many building made from Sandstone Plaster made from rock Gypsum Food seasoned & preserved with Rock salt / Halite Snow & ice on roads melted with Rock salt / Halite Important energy reserves – petroleum & natural gas – Farmers use ag lime treat acidic soil from Limestone – Fertilizer made from Potassium salts / Phophate rocks Uses Sedimentary Rocks • Fossils most likely to lie in sedimentary rocks – Scientists observe fossils • Piece together information of life long ago – Dinosaurs Metamorphic Rocks UD, C2, S3 pD56-61 Formation of Metamorphic Rocks • Metamorphic rocks not common on the surface – Form inside Earth’s crust – Forces inside Earth lift them up – Weathering wears away rock on top of them • Metamorphism: process when any kind of rock is changed into metamorphic rock – Inside Earth – Intense heat & pressure change properties of rocks – Depends on “parent rock” & amount heat and pressure Formation of Metamorphic Rocks • Metamorphism occurs under two conditions: – Regional metamorphism • Most common – Plates collide with tremendous pressure – Rock crumples and folds forming mountains – Metamorphic rock in their centers – Contact metamorphism • Occurs deep in the crust and under volcanoes – Magma rises and touches rock – Rock “bakes” changing properties Formation of Metamorphic Rocks • Metamorphic rocks classified into two groups – Foliated • Layers or bands you can see – Gneiss – Nonfoliated • Do not appear layered – Marble Processes That Cause Metamorphism • Heat most important cause of metamorphism – Deeper in Earth’s crust, the hotter it gets • 20-60°C hotter per kilometer of depth • If rock gets too hot it melts – Source of igneous rock • Heat breaks chemical bonds allowing new crystallization Processes That Cause Metamorphism • Pressure another cause of metamorphism – Deeper in Earth’s crust, the more pressure there is • Weight of all rock & soil above rock presses down • Crustal movement squeezes rock & bends it – Heat softened the rock already making it easier to bend • Extremely hot water can cause metamorphism – Mineral-rich water near magma (300-500°C) • Minerals added/taken away from rock – Gold, silver, copper often deposited in these rocks • Texture & minerals of rock tell how it was formed Uses of Metamorphic Rocks • Metamorphic rocks used in parts of buildings – Marble used in statues & public buildings • Beautiful & durable – Slate used for roofs, chalkboards, floors, and pavement stones • Splits easily into thin sheets – Talc used for lubrication, cosmetics, dusting powder • From schist easy to make into a powder – Graphite used as pencil “lead” & lubricants • Another mineral from some metamorphic schists The Rock Cycle UD, C2, S4 pD64-67 The Rock Cycle • Rock cycle: shows processes where rocks are formed from each other – A way Earth recycles its rocks • All rock was igneous to begin – Earth was molten rock early in history and it cooled – Wind, water, ice started weathering/eroding rock • Formed sedimentary rock – Heat & pressure deep in earth and millions of years • Changed rock to metamorphic rock – Rocks changing between these three ever since The Rock Cycle • Five main groups of processes – Melting: • All three rock types melt forming magma – Cooling & solidification: • Magma cools forming igneous rock – Weathering, erosion, deposition: • All three rock types form sediments that are deposited – Cementation & compaction: • Sediment is cemented and compacted forming sedimentary rock – Heat & pressure: • All three rock types changed to metamorphic rock The Rock Cycle & Plate Boundaries • Oceanic – Continental Convergent Boundary – Sedimentary rock • Sediment deposited where rivers end – Metamorphic rock • Igneous & sedimentary rock carried down • Rock melted as it continues to sink • Magma rises in cracks & bakes rock around it – Igneous rock • Rising or erupting magma cools How Fossils Form Additional Slides How a Fossil Forms • Most fossils form when living things die. How a Fossil Forms • Next, the organism is buried by sediment. How a Fossil Forms • The sediment slowly hardens into rock and preserves the shapes of the organisms. How a Fossil Forms • The sediment slowly hardens into rock and preserves the shapes of the organisms.
