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Igneous Rocks

Igneous Rocks. Chap. 5. What are igneous rocks? Identifying igneous rocks. Objectives. What are igneous rocks? – 5.1. compare and contrast intrusive and extrusive rocks describe the composition of magma discuss the factors that affect how rocks melt and crystallize. Rhyolite breccia.

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Igneous Rocks

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  1. Igneous Rocks Chap. 5 • What are igneous rocks? • Identifying igneous rocks

  2. Objectives What are igneous rocks? – 5.1 • compare and contrast intrusive and extrusive rocks • describe the composition of magma • discuss the factors that affect how rocks melt and crystallize Rhyolite breccia

  3. Definition

  4. Igneous Rocks Rocks formed when magma crystallizes. ‘Ignis’ = fire

  5. Types of Igneous rocks

  6. Types of Igneous rocks • Extrusive – fine grained rocks that cool quickly, on Earth’s surface Basalt

  7. Types of Igneous rocks • Intrusive – -grained rocks that cool , the Earth

  8. Types of Igneous rocks • Intrusive – coarse-grained rocks that cool slowly, under the Earth Granite

  9. Magma composition

  10. Magma composition • Molten rock

  11. Magma composition • Molten rock • Gases

  12. Magma composition • Molten rock • Gases • Mineral crystals

  13. Magma composition • Molten rock • Gases • Mineral crystals • Magma Classifications

  14. Magma composition • Molten rock • Gases • Mineral crystals • Magma Classifications • Basaltic – 50% SiO2

  15. Magma composition • Molten rock • Gases • Mineral crystals • Magma Classifications • Basaltic – 50% SiO2 • Andesitic – 60% SiO2

  16. Magma composition • Molten rock • Gases • Mineral crystals • Magma Classifications • Basaltic – 50% SiO2 • Andesitic – 60% SiO2 • Rhyolitic – 70% SiO2

  17. Magma Formation is Influenced by

  18. Magma Formation is Influenced by • Temperature (increases with depth)

  19. Magma Formation is Influenced by • Temperature (increases with depth) • Pressure (as pressure ↑, melting pt. ↑)

  20. Magma Formation is Influenced by • Temperature (increases with depth) • Pressure (as pressure ↑, melting pt. ↑) • H2O content (more H2O, melting pt. ↓)

  21. Magma Formation is Influenced by • Temperature (increases with depth) • Pressure (as pressure ↑, melting pt. ↑) • H2O content (more H2O, melting pt. ↓) • Mineral content Granite has higher water content so it melts at a temperature

  22. Magma Formation is Influenced by • Temperature (increases with depth) • Pressure (as pressure ↑, melting pt. ↑) • H2O content (more H2O, melting pt. ↓) • Mineral content Granite has higher water content so it melts at a lower temperature

  23. Melting Rocks

  24. Melting Rocks • Partial melting Some minerals melt while others remain solid

  25. Melting Rocks • Partial melting HEAT Some minerals melt while others remain solid

  26. Melting Rocks • Partial melting • Fractional crystallization As liquid rock cools certain minerals crystallize before others

  27. Melting Rocks • Partial melting • Fractional crystallization COOLING As liquid rock cools certain minerals crystallize before others

  28. Bowen’s Series A chart that shows how minerals crystallize when cooled

  29. Bowen’s Series • Two paths

  30. Bowen’s Series • Two paths • Continuous path for feldspars

  31. Bowen’s Series • Two paths • Continuous path for feldspars • Stepwise path for Fe/Mg minerals

  32. Bowen’s Series • Two paths • Both paths end with Si and O – the last minerals to crystallize

  33. Intrusions

  34. Intrusions • Quartz (SiO2) finds way into rock veins Quartz vein

  35. Intrusions • Quartz (SiO2) finds way into rock veins • Intruded masses of rock cool in layers, often carrying metals (gold, silver, and platinum)

  36. The End

  37. Objectives Classifying Igneous Rocks 5.2 Basalt • Classify different types and textures of igneous rocks • Recognize the effects of cooling rates on the grain sizes • Describe some uses of igneous rocks

  38. Where rock forms

  39. Where rock forms • Intrusive forms .

  40. Where rock forms • Intrusive forms under surface. • Extrusive forms .

  41. Where rock forms • Intrusive forms under surface. • Extrusive forms above surface.

  42. Rock’s composition

  43. Rock’s composition • Felsic – silicon-rich, light colored Granite

  44. Rock’s composition • Felsic – silicon-rich, light colored • Mafic – iron & magnesium rich, dark colored Gabbro

  45. Rock’s composition • Felsic – silicon-rich, light colored • Mafic – iron & magnesium rich, dark colored • Ultramafic – very high levels of Fe & Mg Peridotite

  46. Texture • Phaneritic has coarse grains Granite

  47. Texture • Aphanitic is fine-grained Basalt

  48. Texture • Vessicular – has tiny holes Vessicular Basalt

  49. Texture • Glassy – has no visible grains Obsidian

  50. Texture • Porphyritic – has large grains surrounded by smaller grains Andesite

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