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Igneous Rocks

Igneous Rocks. The root word ignis comes with the latin word for “fire” Igneous rocks form from crystallization of magma (below Earth’s surface) or lava (above Earth’s surface). Igneous Rocks. Magma is a slushy mix of molten rock, gases, and mineral crystals

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Igneous Rocks

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  1. Igneous Rocks • The root wordigniscomes with the latin word for “fire” • Igneous rocks form from crystallization of magma (below Earth’s surface) or lava (above Earth’s surface)

  2. Igneous Rocks • Magma is a slushy mix of molten rock, gases, and mineral crystals • The main compound in magma is silica (SiO2) • Controls melting point and viscosity how well lava flows

  3. Igneous Rocks • It takes temperatures of 800-1200°C deep within the Earth to melt rocks • The main factors involved in magma formation are: • Temperature • Pressure • Mineral Content • Water Content

  4. Igneous Rocks • As depth beneath the Earth increases, pressure increases • Melting point increases because particles are more densely packed

  5. Igneous Rocks • Different substances = Different melting points = Partial Melting • As each group of minerals melts, different elements are added to magma, changing its composition

  6. Igneous Rocks • During cooling, the last minerals to melt are the first to crystallize. This called fractional crystallization. • Why?

  7. Igneous Resources • Minerals that contain useful substances that can be mined for profit are called ores. • Due to fractional crystallization, igneous ore deposits are often found in veins. We mine valuable substances such as gold, silver, lead, and copper. • Pegamites: large veins • Kimberlites: small veins (diamonds)

  8. What do we use igneous rocks for?

  9. Igneous Rock Summary Questions 1. Compare and contrast the process of baking cookies to the formation of igneous rocks: • How is the dough both similar to and different from magma? • Describe the viscosity of the dough that we made in class. • How does magma change when it is exposed to temperature change. How is this similar to and different from how the cookie dough changes when exposed to temperature change? 2. What type of igneous rock are you eating? Describe the texture, hardness, grain size, composition, etc and why it represents that type of igneous rock. 3. Sometimes similar minerals clump together in a rock sample. Do you see this happen in your cookie? Provide a hypothesis for why this might happen.

  10. Sedimentary Rocks

  11. Why did this happen?

  12. How do rocks on the Earth’s surface change? • Weathering= rocks and sediments break down • Erosion= smaller pieces are moved to new locations • Three types: • Physical (mechanical) • Chemical • Biological

  13. What is physical weathering? • NO changes in composition • Size and shape change • Factors: • Temperature • Frost wedging: water freezes and expands, cracking rocks • Pressure • Exfoliation: pressure of overlying rocks are removed, underlying rocks can expand

  14. Physical Weathering Temperature Pressure

  15. What is chemical weathering? • Mineral composition CHANGES • Chemical reaction occurs • NEW minerals form • Agents: • Water Hydrolysis • Oxygen Oxidation • Carbon Dioxide ex: cave • Acid ex: acid rain

  16. What is biological weathering? • Living organism cause changes in rocks or sediment • Ex: tree roots growing around a rock and splitting it • Ex: humans displacing or removing rock surfaces

  17. What affects the rate of weathering? • CLIMATE • Chemical weathering is more common/faster in areas of warm temperatures and high rainfall • Ex: “Painted Desert” of Arizona/New Mexico • Physical weathering is more common/faster in areas of cool, dry climate • Ex: NC mountains

  18. What are sediments? • Even though igneous rocks are the most common in Earth’s crust, most of Earth’s surface is covered in sediment. • Sediments: pieces of solid rock material re-deposited on Earth’s surface by forces (wind, water, ice, gravity, precipitation, etc.)

  19. How do sediments become sedimentary rocks? (Part 1) • Weathered particles get moved downhill (erosion) • Get laid down/sink (deposition) • Deposits become layered (sorting) • Layers stack up on top of each other (burial) • These processes add material to sedimentary basins

  20. How do sediments become sedimentary rocks? (Part 2) • As burial occurs, layers are subjected to greater heat and pressure • These conditions cause lithification • lithos = stone • Sediments  Sedimentary Rocks • Two steps: • Compaction • Cementation

  21. What is a sedimentary basin? • Newest, smallest particles • 3rd oldest layer • 2nd oldest layer • Oldest, largest particles • Depression in Earth’s crust

  22. What do sedimentary rocks look like? • Bedding! • Horizontal layers • Graded bedding • Bigger on the bottom • Cross-bedding • Slanted layers

  23. How are sedimentary rocks classified? • By formation • Organic sedimentary rocks (from once living things) • Chemical sedimentary rocks (evaporites) • Clastic sedimentary rocks (loose deposits on Earth’s surface)—Most common

  24. Metamorphic Rocks • Change • Form • You tell me…what factors cause chemical and physical changes in rocks??

  25. What is contact metamorphism? • What is hydrothermal metamorphism? • Molten rock comes in contact with solid rock • High temperature/low pressure • Hot water comes in contact (reacts with) rock • High temperature/moderate pressure • Deep sea vents/volcanoes

  26. How are metamorphic rocks classified? Foliated Non-Foliated

  27. How are metamorphic rocks classified? Foliated Non-Foliated

  28. What are porphyroblasts? • New metamorphic minerals grow LARGE while surrounding minerals remain small

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