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- 1. The Rock Cycle An Exploration of the World Under Your Feet
- 2. What is a “Rock”? • Rock: is a fairly general term that refers to any solidified mixture of inorganic or fossilized organic materials. – There are a multitude of extremely diverse rock types that can be differentiated and classified based upon their elemental composition, physical properties, and formation mechanism. • Mineral: inorganic solid with a specific internal structure and a definite chemical composition. – Minerals are the basic building blocks of rock. – Almost all minerals contain some combination of the following elements: 2 • Oxygen - O • Silicon - Si • Magnesium - Mg • Iron - Fe • Aluminum - Al • Calcium - Ca
- 3. 3 3 Major Rock Types • Igneous – Formed from the solidification of molten rock (magmaor lava). • Sedimentary – Formed at the Earth’s surface from the accumulation and cementation of fragmented pieces of older rock produced by weathering. • Metamorphic – Rocks that have undergone physical changes as a result of exposure to extreme pressure, temperature and fluids.
- 4. The Rock Cycle • Law of Conservation of Matter: Matter cannot be created or destroyed it can only change forms. • This fundamental law of the universe applies to the chemical elements that make up the earths rock. • Particular rock formations are created and destroyed many times over geologic timescales but the chemical material itself is recycled over and over again through the rock cycle. 4
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- 7. Types of Igneous Rock • Igneous (ignis= fire) – Formed from the solidification of molten rock (magma or lava). • Magma: is molten rock below the surface of the earth. • Lava: is molten rock that has been extruded on to the surface of the earth. – Igneous Rocks are generally classified based on where in the earth crystallization takes place. • Plutonic (Intrusive): Magma slowly cools and crystallizes below the earths surface. – Since the cooling process is very slow intrusive igneous rocks have very large crystals (coarse grained). • Volcanic (Extrusion): Lava cools quickly at the surface of the earth. – Since the cooling process is very fast extrusive igneous rocks have very small crystals (fine grained). 7
- 8. Igneous Classification: Texture Volcanic Glass: Extrusive igneous rock formed when lava comes in contact with water and cools instantly. Appears glass-like. Example: Obsidian 8
- 9. Igneous Classification: Texture Aphanitic: Typically form from lava which crystallizes rapidly on or near the Earth’s surface. • Because extrusive rocks make contact with the atmosphere they cool quickly, so the minerals do not have time to form large crystals. • The individual crystals in an aphanitic igneous rock are not distinguishable to the naked eye. • Example: Basalt 9
- 10. Igneous Classification: Texture • Phaneritic: (phaner = visible) textures are typical of intrusive igneous rocks, these rocks crystallized slowly below the Earth's surface. • As a magma cools slowly the minerals have time to grow and form large crystals. • The minerals in a phaneritic igneous rock are sufficiently large to see each individual crystal with the naked eye • Example: Fine Grain Granite 10
- 11. Igneous Classification: Texture • Pegmatitic: Texture that occurs during very slow magma cooling when some minerals may grow so large that they become massive. • Crystal size ranges from a few centimeters to several meters. • Example: Large Grain Granite 11
- 13. Igneous Classification: Composition • Felsic Rocks: Are those that are light in color and are mostly made up of feldspars and silicates. Low Density. • Intermediate Rocks: fall somewhere in between being Felsic and Mafic. Intermediate Density. • Mafic Rocks: Are darker colored and are mostly made up of magnesium and iron. – Ultramafic Rocks: Very dark colored. 13
- 14. Fig. 2.9 MAGMA
- 20. Weathering, Erosion, and Deposition Weathering – the breakdown of rocks into smaller pieces, called sediments. Transport (Erosion)– the process where the sediments are carried by wind, gravity, glaciers, man, and running water. Deposition – the process whereby these sediments are released by their transporting agents (dropped). Weathering breaks down the rocks, erosion moves the particles, and deposition drops the sediments in another location.
- 21. Types of Weathering • There are two main types of weathering: – Physical Weathering: the breakdown of rocks and minerals into smaller pieces without a change in chemical composition. – Chemical Weathering: the breakdown of rocks and minerals into smaller pieces by chemical action. The rocks breaks down at the same time as it changes chemical composition. The end result is different from the original rock.
- 23. Frost Wedging: rock breakdown caused by expansion of ice in cracks and joints. - Water expands when it freezes
- 24. Exfoliation: As previously buried rock formations are exposed they experience a decrease in confining pressure causing them to expand and fall off in parallel sheets.
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- 26. Plant and Animal Activity • Lichens and mosses grow on rocks. – They wedge their tiny roots into spores and crevices. – When the roots grow, the rock splits. • Larger trees and shrubs may grow in the cracks of boulders. • Ants, earthworms, rabbits, woodchucks, and other animals dig holes in the soil. – These holes allow air and water to reach the bedrock and weather it. 26
- 27. There Are 3 Types of Chemical Weathering: Oxidation– oxygen combines with the elements in the rock and it reacts. This the scientific name for rust. Hydration– water can dissolve away many earth materials, including certain rocks. Carbonation– carbon dioxide dissolves in water to form carbonic acid. This makes acid rain which chemically weathers (dissolves) rocks. Other acids also combine with water to make acid rain.
- 29. 2.Particle Size – Larger particles weather slower and smaller particles weather at a faster rate. There are 4 factors that effect the rate of weathering: 1.Surface Area (exposure) - Exposing more surface area will increase the rate of weathering. 3.Chemical Composition (what a rock is made of) – Certain rocks and minerals are naturally weaker than others, while others are more resistant (stronger). 4. Climate – Warmer, moister climates have the most weathering. Heat & Water speed up all chemical reactions. This is the most important factor in weathering.
- 31. Transport and Deposition • Sediments are transported away and deposited in other locations. • These depositional environments are often layered or stratified. – Older sediments at the bottom – Newer sediments on top • One can deduce the transport mechanism based upon: – Grain Size – Sorting – Roundness 31
- 32. Grain Size • Based on the fundamental idea that as the amount of weathering increases a rock will break into smaller and smaller pieces. • The grain size a sediment tells you how much weathering it has undergone. – Also tells you the strength of the transport process. • Wentworth Scale 32
- 33. Roundness As weathering increases a sediments well defined sharp edges wear away (angularity decreases) and the rock becomes more rounded 33
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- 36. Sorting • Sorting describes the distribution of grain size of sediments. • Very poorly sorted indicates that the sediment sizes are mixed (large variance) • Well sorted indicates that the sediment sizes are similar (low variance). • The degree of sorting may also indicate the energy, rate, and/or duration of deposition, as well as the transport process responsible for laying down the sediment. 36
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- 38. You can identify which agent of erosion transported each sediment by looking at a few characteristics: Running Water – sediments that have been transported through running water appear rounded and smooth and are deposited in sorted piles. Glaciers – sediments that have been transported by glaciers appear scratched, grooved, and are deposited in completely unsorted piles, because they were dropped during melting. Also, boulders can only be transported by glaciers. Wind - sediments that have been transported by wind are appear pitted (random holes) and frosted (glazed look) and are deposited in sorted piles. Only very small particles can be transported by wind. Gravity – sediments that are transported by gravity are found in piles at the bottom of cliffs or steep slopes. They appear angular and unsorted.
- 41. Classifying Sedimentary Rocks • Sedimentary rocks are classified by their composition and by the manner in which they formed. • The three types of sedimentary rocks are – Detrital: Sedimentary rocks that are made from the broken fragments of other rocks. – Chemical (Evaporite): Mineral crystal formed when water evaporates and leaves behind any dissolved (chemically weathered) minerals. – Organic: Sediment formed from the remains of dead plants and animals.
- 42. Compaction and Cementation Forms Detrital Sedimentary Rocks • Where sediments are deposited, layer upon layer builds up. • Pressure from the upper layers pushes down on the lower layers. • If the sediments are small, they can stick together and form solid rock. This process is called compaction. • If sediments are large, like sand and pebbles, pressure alone can’t make then stick together – Large sediments have to be cemented together. • As water moves through soil and rock, it picks up materials released from minerals during weathering. • The resulting solution of water and dissolved materials moves through open spaces between sediments cementing them together.
- 45. Geodes Formed when air pockets in rock fills with water forming evaporite crystals. 45
- 46. • Form from Biogenous Ooze – >30% of debris from planktonic organisms – Calcareous oozes (CaCO3) • Shells of foraminifera (zooplankton) and coccolithophorids (phytoplankton). • Accumulate on seafloor. • Forms hard limestone under pressure Biologic Sedimentary Rocks
- 50. Metamorphic Rocks • Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphismwhich means "change in form". • The original rock is subjected to heat (temperatures> 150 °C) and pressure (>1500 bars)causing profound physical and/or chemical change. 50
- 51. Types of Metamorphism • Contact Metamorphism: Rock that comes in close contact with magma and undergoes metamorphism as a result of the extreme temperature. • Regional Metamorphism: A large volume of rock is buried in the crust and exposed to high temperature and pressure. 51
- 52. Gem Stones • Many precious minerals form at metamorphic zones. • Minerals with low melting points liquefy, while those with higher melting points remain solid. – These liquefied minerals accumulate in voids, solidify, and become precious minerals. 52
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- 54. 54 MAGMA Volcanic IGNEOUS Plutonic SEDIMENT SEDIMENTARY METAMORPHIC Uplift Burial Increased P&T Melting Crystallization Weathering Erosion Transport DepositionCan you see any shortcuts?
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- 57. • The rock cycle demonstrates the relationships among the three major rock groups • It is powered by the interior heat of the Earth • It involves processes on the Earth’s surface as well as the Earth’s interior • It connects the “hydrologic cycle” with the “tectonic cycle”. In Conclusion…
- 60. 60 Major Rock Groups • Igneous – Formed from the solidification of molten rock (magmaor lava). – Plutonic (intrusive):slow cooling and crystallization – Volcanic (extrusion): quick cooling at the surface • Sedimentary – Formed at the Earth’s surface from the accumulation and cementation of fragmented pieces of older rock produced by weathering. – Clastic (Mineral Fragments or grains, clays) – Chemical (crystalline chemical/biochemical precipitates) • Metamorphic – Rocks that have undergone physical changes as a
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