Geology Week 2 Notes
Geology Week 2 Notes 80176 - GEOL 1010 - 001
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80176 - GEOL 1010 - 001
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This 10 page Class Notes was uploaded by Sarah Canterbury on Monday February 1, 2016. The Class Notes belongs to 80176 - GEOL 1010 - 001 at Clemson University taught by Alan B Coulson in Fall 2015. Since its upload, it has received 35 views. For similar materials see Physical Geology in Environmental Science at Clemson University.
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Date Created: 02/01/16
Lecture 3 – 1/19/16 Geology in The news Seismic activity in Pacific northwest linked to subduction of the Juan de Fuca plate beneath N. America Also explains why there are several volcanos in that area Part 1 – Chemistry Review & Mineral Basics Rocks and minerals Why do we care? They’re everywhere- in the food we eat, construction, valuable Basic Chemistry Atoms- basics building blocks of all matter Find ways to use them to build different minerals Protons (+), neutrons (), and electrons (-) Atomic number- number of protons in an atom Defines the atom as belonging to a specific element (even if # of electrons and neutrons are different) Element- Several elements are very very rare Chemistry of earth’s crust Oxygen- 46.6%, Silicon- 27.7%, Aluminum- 8.1%, Iron- 5.0%, Calcium- 3.6%, Sodium- 2.8%, Potassium- 2.6%, etc. Part 2- What is a mineral? How do we define something as a mineral? Must meet all 5 criteria: 1- Non-synthetic: must be formed completely in nature on its own 2- Inorganic: any organic substance in automatically ruled out Doesn’t contain any copmonents that would classify it as living 3- Crystalline: very specific pattern for how it’s built Opposite of crystalline- amorphous: random pattern, nothing strongly repeated 4- Solid: not a liquid, gas, or plasma State is determined by T/P conditions Can melt or evaporate, but only considered a mineral in solid form 5- Set chemical composition: can write a chemical formula to describe a mineral Some substitutions occur: out in the real world sometimes may have an element substituting another element in the chemical formula- doesn’t invalidate the rule Part 3- Mineral Properties How do we identify specific minerals? 1- Color: tricky because some minerals come in a wide range of color, so color can be useless 2- Streak: color of the mineral when you grind it up; sometimes streak is a different color than color you see 3- Hardness: how easily can the mineral be scratched Moh’s Scale: a scale from 1-10 describing hardness (1-softest; 10-hardest) For each number on the scale, there’s a mineral to describe that number Tools to determine hardness: Fingernail- 2.5, knife- 5, etc Can be variations because not every pocket knife (or other tools) are universally the same hardness 4- Luster: how shiny/dull the mineral is Metallic- looks like a metal; Vitreous- glassy; Resinous; Greasy; Silky; Dull; Pearly 5- Effervescence: put acid on mineral and it’ll hiss and fizz (start to bubble with strong acids) 6- Crystal Form: shape or form crystal will be in In nature, the mineral wants to form in a specific pattern Ex) If NaCl forms in perfect conditions, it’ll grow in a cube shape 7- Breakage patterns: how the mineral cracks or breaks Fracture: no set pattern to how the pieces break Cleavage: breaks on very flat/smooth surfaces See how many directions it breaks in- cleavage planes 8- Taste 9- Smell 10-Magnetic Part 4- Common Mineral Groups Minerals are grouped by a common anion (negatively charged particle) How to classify and how to identify are two different things Many groups exist Mineral Groups Sulfides: Sulfur (S) is common anion Oxides: Oxygen (O) is common anion Both very similar because chemical formula is simple (metal + anion) Sulfides and oxides are big targets for mining Sulfates: SO4is common anion Used in construction for dry wall and plasters Phosphates: PO 4is common anion Used in fertilizer and is primary mineral in bones and teeth Carbonates: CO 3is common anion Organism shells, coral, in deep part of ocean there are tiny shells from dead organisms Effervescence Silicates: SiO4is common anion Tetrahedron- has 4 faces (like a pyramid) Very common and abundant Polymerization: take two and link them together 2 tetrahedra never share more than 1 oxygen atom between them Types of Silicates Sub-groups depend on how tetrahedra polymerize - Island Silicates: no polymerization at all - Chain Silicates: a strand or chain of tetrahedra Can have two chains linked in the center - Sheet Silicates: polymerization seems to be spreading in a two-dimensional sheet of tetrahedra Sometimes hard to visualize Bonds between are very weak; therefore, layers are easy to peel apart - Framework Silicates: tetrahedra are polymerized in all directions Bonded at several different angles Contain some of most abundant minerals on earth Part 5- The Rock Cycle “Rock” and “Mineral” are not interchangeable Rock- something made up of 1 or more minerals and maybe some other stuff Only 3 different types of rock if formed on this planet Differentiated by how they form Linked via the Rock Cycle 1) Magma: liquid rock, rocks heated up to point where they melt If you cool it down enough, it’ll turn solid When cooled, forms igneous rock 2) Weathering: exposed to several processes on the surface that break and wear down the rock 3) Erosion: picks up debris/broken down rock and moves it to new location (via rivers or wind) 4) Deposition: the rocks are deposited – stop moving 5) Lithification: turn it into stone Forms sedimentary rock- often form in layers 6) Metamorphism: forms metamorphic rocks by varying temperature and pressure 7) Increase to melting point and forms magma again Can have shortcuts- not a 1 point cycle Lecture 4—1/21/16 Geology in the News 21000 homes in Flint, Michigan have lead contamination in their drinking water Has been going on for a while, so major political issue Lead is very dangerous, especially for children Part 1—Magma Why do we care? 1- Hazardous- can threaten people’s safety and property with volcanic activity Try to predict eruptions and keep people safe 2- Igneous rocks are very useful construction material Very durable, but can be very expensive What is magma? Magma: liquid rock, when liquid rock is underground Lava: liquid rock, when liquid rock is above ground Melting Processes How to melt rock: 1- Temperature: minerals all have fixed melting points, which are very high (500-600 Partial melting: Most rocks contain several minerals, so a rock won’t melt all at once 2- Wet Melting: addition of water in a rock will significantly lower melting point Only when rock is saturated down to the crystal level (can’t just splash water onto a rock) 3- Decompression Melting: pressure is important when melting rock; less pressure makes it easier to melt the rock Must consider each of these three things when talking about melting point of rocks Magma Composition Gases: don’t see it right away, but it’s there Very important when talking about volcanic eruption SiO : such important component, that it’s used to identify igneous rock Key property to classify which type of magma 1- Basaltic Magma: most common type of magma Source: generated in the Mantle Dry Magma: basaltic magma doesn’t have a high water content 50% SiO2 content Other 50% a combination of other materials 1100 deg C: hotter than the other types Not restricted to any specific location 2- Andesitic Magma Source: Mantle Only found in very specific locations Found along coasts of Pacific Ocean—known as ring of fire Why found in this specific location? Plate Tectonics- forms at subduction zones 60% SiO2 content Cooler than Basaltic—1000 deg C Still considered dry magma, but has higher water content than Basaltic 3- Rhyolitic Magma Formed at a shallower depth- crust Cooler magma: 700-800 deg C 70% SiO2 content: highest silica content—crust contains a lot of silica Wet Magma—has high water content Study Hint: instead of trying to memorize everything about the different types of magma, try to understand how all the properties are linked Freezing of Magma Crystallization: freezing; liquid to solid Partial Freezing: freezing won’t all happen at 1 temperature There will be a transition with a range of temperatures Equilibrium Crystallization: all the magma freezes, so nothing changes about the chemical composition Fractional Crystallization: remove something from the equation while freezing Composition changes as magma freezes Crystallization Minerals form in a specific order as magma cools Bowens Reaction Series Describes which minerals form at which temperatures **see the diagram on the lecture slides online** Discontinuous Branch: as you lower the temperature, you discontinue the process of making one mineral, and begin the process of making another Continuous Branch: dealing with minerals that form under a bigger range of temperatures, but as it does so, the chemical composition will change slightly Plagioclase: high temperatures = calcium rich, but as you decrease the temperature, it becomes more sodium rich Part 2—Igneous Rock Two broad types: 1- Plutonic (Intrusive): formed below the surface of the earth; froze before it reached the surface 2- Volcanic (Extrusive): formed above the surface of the earth; erupts, then freezes 2 Properties needed to identify igneous rock: 1- Texture: how large are the mineral crystals 2- Composition: what mineral crystals are actually present Plutonic Rocks Plutons: any large body of plutonic rock Dikes and sills: both long and narrow bodies of igneous rock Dikes are vertically oriented and sills are horizontally oriented (To remember: sills are oriented like a window sill) Laccoliths: dome or blister shape; magma builds up and tries to force its way up, but gets stuck Batholith: extremely large plutons Don’t have a specific shape, and aren’t organized in a specific way Mt. Rushmore is carved out of a batholith (and a small one on batholith scale) Textures of Intrusive Rocks Pegmatitic (pegmatite): has extremely large crystals in the rock (at least 1cm diameter) Phaneritic: crystals will be smaller than 1cm diameter, but can still identify crystals Composition of Intrusive Rocks Color index: the color of the rock can indicate the composition of the rock Felsic: a lot of white, pink, and/or red in the rock Intermediate: equal mix of light and dark in the rock equally distributed Mafic: dark colors, black and brown in the rock Silica content drops Ultramafic: green and/or yellow colored rock Keep in mind: color index is shortcut; therefore, it will sometimes fail Texture of Extrusive Rocks Porphyritic: Some crystals are big, some are small Phenocrysts: bigger crystals Will form when starts cooling below ground, and finishes cooling on the surface Aphanitic: all the crystals are very small; can’t see without magnification Glassy: rock has a glassy texture Vesicular: have many little holes or pores all over the rock When gas gets trapped in the magma as it freezes
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