Rocks, Rock Resources & Rock Cycle (Chapter 3, 15) Arches Nat’l Park, Utah Yosemite Nat’l Park, CA http://earth-pages.co.uk/2012/11/22/a-glimpse-of-the-hadean/amitsoq-gneiss-2/ Banded Iron, MI Amitsoq gneisses, West Greenland Mineral and Rock Resources Virtually everything we use or build or create in modern life involves rock, mineral and fuel resources taken from the Earth A mineral or rock resource refers to any material of value that is derived from rocks or minerals. Observe the following rocks. How are they different? Major Rock Types Rock Type General Description Common Examples Igneous Rocks that form by crystallizing from magma or lava; crystalline Granite, Basalt Sedimentary Rocks formed from sediments (fragments of rocks, minerals, or animal or plant material) at low temperatures Sandstone, limestone Metamorphic Existing rock that changes form due to exposure to high heat, pressure and/or chemical fluids. Marble, slate, quartzite Igneous Rocks • Rocks that form by crystallizing from magma – Magma = molten rock below surface – Lava = exposed on surface • Characterized by: – texture (crystal size) – composition (color, % silica) What Earth processes can form minerals? • Crystallization – Melt to solid (magma or lava hardens) • Precipitation= saturated solution • Salts from solution in water • Saturated water (groundwater) • Temperature change • Hydrothermal, metamorphism • Weathering= physical and/or chemical http://www.iflscience.com/environment/wat ch-salt-cubes-form-dead-sea Examples of Igneous Rock Resources Pegmatite (Plutonic Igneous Rock) Feldspar for ceramics Hydrothermal Tourmaline for radio equipment Diamonds from Kimberlite pipes! Salts, gases, metals Observe these igneous rocks, what physical features will you use to classify them? 05.02.a1 Igneous rocks textures Igneous Rocks textures Volcanic=lava Cooling of melted “rock” or lava above earth surface Fast cooling Cooling of melted “rock” or magma below earth surface Plutonic=magma Slow cooling Why the crystal-size variation? Granite Basalt Microscopic photos Phaneritic Aphanitic Extrusive or volcanic Extrusive or volcanic intrusive What controls these textures? Next: Kahoot.it Igneous rocks’ textures explain how fast and where the melt cooled https://mediaplayer.pearsoncmg.com/assets/se cs-geology-SmartFigures-Igneous_Textures Igneous rocks have interlocked Minerals (even if invisible to naked eye) “Siblings in law” Major Rock Types Rock Type General Description Common Examples Igneous Rocks that form by crystallizing from magma or lava; crystalline Granite, Basalt Sedimentary Rocks formed from sediments (fragments of rocks, minerals, or animal or plant material) at low temperatures Sandstone, limestone Metamorphic Existing rock that changes form due to exposure to high heat, pressure and/or chemical fluids. Marble, slate, quartzite Sedimentary Rocks: Rocks formed from sediment lithification at low temperature Earth’s Exposed Surface is covered mostly by sediment and sedimentary rocks Sediment laden drainage, Betsiboka River, Madagascar Where does sediment come from? Steps to Sediment 1. Weathering= physical and/or chemical breakdown of rocks and minerals 2. Erosion=movement of sediments Weathering Erosion Weathering Formation of Sediment by… physical or mechanical weathering chemical weathering Animation: http://ees.as.uky.edu/sites/default/files/elea rning/module07swf.swf Steps to Sediment 1. Weathering= physical and/or chemical breakdown of rocks and minerals 2. Erosion=movement of sediments Weathering Erosion How does loose sediment become rock? ? Steps to Sediment 3. Deposition-continental shelves, lake basins, dry deserts, rivers Ultimate Fate: Burial and conversion to sedimentary rock -compaction and cementation (lithification) Lithification = Clastic Rocks Clastic or detrital sedimentary rocks are classified based on sediment size Table 3.3a Chemical Sedimentary Rocks • Some sedimentary rocks consist of crystals formed from precipitation or growth from solution. • Ex. Limestone (composed of calcite (CaCO3) – Deposited from fresh or salt water • Ex. Rock salt (composed of halite (NaCl) – Deposited when salt water is isolated from an ocean and dries up Fossiliferous limestone US Evaporite Deposits: Chemical Sedimentary Rocks Sedimentary Organic Rocks • Made from organic carbon – Coal – Altered remains of fossil vegetation • Accumulates in lush tropical wetland settings • Requires deposition in the absence of oxygen Ripple marks on a sandstone (clastic sedimentary rock) Sedimentary Rocks provide information about environment of deposition… Sedimentary Rocks …and about life that existed during a specific time on Earth Examples of Sedimentary Rock Resources Limestone Salts Banded iron formations, Marquette, MI Gypsum Gypsum Rock, Grand Rapids Gypsum Mine Major Rock Types Rock Type General Description Common Examples Igneous Rocks that form by crystallizing from magma or lava; crystalline Granite, Basalt Sedimentary Rocks formed from sediments (fragments of rocks, minerals, or animal or plant material) at low temperatures Sandstone, limestone Metamorphic Existing rock that changes form due to exposure to high heat, pressure and/or chemical fluids. Marble, slate, quartzite Metamorphic Rocks Examples of Metamorphic Rock Resources Graphite Slate rock (roof & tiles) Gems (garnet) What is Metamorphism? • Change in form (composition & texture) – Heat – Pressure – Chemical Fluids • Why? – Rocks adjust to become more stable Metamorphism does NOT occur by melting!!! ? Metamorphism Causes: 1.Texture changes 2.Crystal size increases 3.Mineral assemblages change Metamorphic Rocks Classification Foliated Rocks • Slate • Phyllite • Schist • Gneiss Typically Non-foliated • Marble • Quartzite Metamorphic Effects Foliation: Flat arrangement Of minerals Causes deformation Granite (Igneous Rock) Gneiss (Metamorphic Rock) Slate • Well-developed foliation • Tends to have a dull appearance • Crystals too small to see. • Metamorphism from fine grained sedimentary rocks (mudstone, siltstone) or volcanic ash. Chalkboards Read Case Study St Francis Dam (page 101) Metamorphic Effects Non-foliated Limestone (Sedimentary Rock) What is marble used for? Marble (Metamorphic Rock) Figure 2-21 Kahoot The Rock Cycle Animation •Loop that involves the processes by which rock types transform to another. •Illustrates the various processes and paths as Earth materials change both, below and above the Earth’s surface https://mediaplayer.pearsonc mg.com/assets/secsgeology-SmartFiguresThe_Rock_Cycle Geologic Time Scale X X Meaning: zoic=life Paleo= ancient Meso=mid Ceno= recent Archean=old Protero=before © 2011 Pearson Education, Inc. X- previous divisions Three Rock Laws • Based on some basic principles: – Law of Superposition – Law of Original Horizontality – Law of Cross-Cutting Relationships These principles help geologists decipher the sequence of events, paleo-environments & correlate rock layers! Law of Superposition • Developed by Nicolaus Steno in 1669 • In an undeformed sequence of sedimentary rocks (or layered igneous rocks), the oldest rocks are on the bottom. • Applies also to lava flows and ash beds from volcanic eruptions Highest layers are youngest layers in sequence River deposits are youngest (not part of the layered sequence) Lowest rock layers are oldest Upper layers are youngest Observe these layers. Which is oldest and which is youngest? Principle of Original Horizontality • Layers of sediment are generally deposited in a horizontal position. • Rock layers that are flat have not been disturbed. Time Younger Units Deposited on Older Units Tan sediment deposited over older rock Red layers deposited over tan Third layer is youngest and is on top 09.01.a Superposition Is Well Illustrated by the Strata in the Grand Canyon © 2011 Pearson Education, Inc. Rocks can experience deformation: 1) Fractured 2) Faulted 3) Folded Normal Fault in Iran Source: Facebook/Geomorphological Features Principle of Cross-cutting Relationships • Younger features (example: faults, igneous intrusions) cut across older features. © 2011 Pearson Education, Inc. Younger Rock or Feature Can Crosscut an Older Rock or Feature Determine which rock or feature is younger in each image Limestone Tan dikes Fractures 09.01.a Dark igneous rock Inclusions • Piece(s) of rock that is/are enclosed within another rock. • Younger rock/feature can contain pieces of older rocks or features. Unconformity • Break (or gap) in the rock record produced by erosion and/or nondeposition of rock units. • Represent significant geologic events in history • Three types: –Angular –Disconformity –Nonconformity What Does an Unconformity Represent? Limestone folded and later eroded by rivers Deposit layers, like gray limestone Sediment deposited on top of eroded surface forming an angular unconformity Unconformity 09.03.a Angular unconformity tilted rocks are overlain by flat-lying rocks Animation: http://www.classzone.com/books/earth _science/terc/content/visualizations/es 2902/es2902page01.cfm?chapter_no= visualization Nonconformity • Metamorphic or igneous rocks in contact with sedimentary strata • Uplift, weathering and erosion • Sediment deposition Animation: http://geologyguy.com/teaching/iac/animations/ angular_unconformity.htm How Does a Nonconformity Form? Non-layered rock uplifted and eroded Erosion surface buried by sediment Sandstone Granite Younger Rocks and Features Can Cause Changes Along Contacts with Older Rocks Observe the boundaries between different rock types Lava flow Dark dike Gray conglomerate Older rock Baking along contacts Baking along base of lava flow (but not on top) Sill can bake rocks below and above Kahoot 09.01.a Disconformity *Strata on either side of the unconformity are parallel *Erosion and/or crustal movements *Hard to identify Animation: http://www.wwnorton.com/colleg e/geo/egeo2/content/animations /10_4.htm How Does a Disconformity Form? Weathering erodes surface Deposition of horizontal layers Eroded surface covered by later sediment 09.03.c Observe two disconformities in this photograph 09.03.c4 Mississippian Limestone Disconformity 2 Devonian Formation Cambrian Limestone Disconformity 1 Unconformities in the Grand Canyon https://mediaplayer.pearsoncmg.com/asset s/secs-geology-SmartFiguresLabs on Rocks, etc Geologic_Histories © 2011 Pearson Education, Inc.
