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Understanding Igneous Rocks: Types, Formation, and Characteristics

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This chapter explores igneous rocks, detailing their formation from crystallized magma including definitions and types. It distinguishes between intrusive rocks that cool slowly beneath the Earth’s surface, like granite, and extrusive rocks that cool quickly on the surface, such as basalt. Key factors affecting magma composition, melting, and crystallization are discussed, along with the significance of gas content and temperature. The chapter also covers the texture of igneous rocks, helping readers understand practical applications and the environmental conditions under which these rocks form.

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Understanding Igneous Rocks: Types, Formation, and Characteristics

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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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