Petrologi 5-nomenklature

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Petrologi 5-nomenklature

  1. 1. Igneous Rocks Igneous Rocks  “Ignis” means fire  Rocks that are formed from cystallization of magma  Magma is molten rock  Lava is magma that is on the Earth’s Surface
  2. 2. Igneous Rocks  Two Types of Igneous Rocks  Extrusive (Exterior)  Intrusive (Interior) Igneous rocks that solidify into rock beneath Earth’s surface Coarse Grained Cool Slowly Granite
  3. 3. Extrusive Igneous Rocks Extrusive (Exterior)  Igneous rocks that solidify into rock on Earth’s surface  Fine Grained  Cool Quickly
  4. 4. Intrusive Igneous Rocks Intrusive (Interior)  Igneous rocks that solidify into rock beneath Earth’s surface  Coarse Grained  Cool Slowly  Granite
  5. 5. Igneous Rock Formation
  6. 6. Igneous rocks: Igneous textures Texture a. size b. shape c. arrangement of interlocking crystals
  7. 7. cooling rate crystal size Slow cooling larger crystals Fast cooling small or no crystals
  8. 8. Fine-grained Large crystals in matrix Coarse-grained Glassy
  9. 9. fast cooling magma/lava forms at or near surface sometimes holes present can’t see individual crystals Fine-grained forms far below surface slow cooling intergrown crystals Coarse-grained magma cooled slowly for a while then erupted minerals crystallize at different temperatures and or rates Large crystals in matrix Glassy very rapid cooling ions unable to unite in orderly crystalline structure
  10. 10. Magmas with high silica content tend to form long chainlike structures - impedes ion transport - increases resistance to flow viscosity
  11. 11. In violent volcanic eruptions, rock fragments ash consolidate molten blobs large angular blocks Pyroclastic rock
  12. 12. Igneous textures  Texture is used to describe the overall appearance of a rock based on the size, shape, and arrangement of interlocking minerals  Factors affecting crystal size Rate of cooling Slow rate promotes the growth of fewer but larger crystals
  13. 13. Igneous textures  Factors affecting crystal size Rate of cooling Fast rate forms many small crystals Very fast rate forms glass Amount of silica (SiO2) present Amount of dissolved gases
  14. 14. Igneous textures  Types of igneous textures Aphanitic (fine-grained) texture Rapid rate of cooling of lava or magma Microscopic crystals May contain vesicles (holes from gas bubbles) Phaneritic Slow (coarse-grained) texture cooling Crystals can be identified without a microscope
  15. 15. Aphanitic texture
  16. 16. Phaneritic texture
  17. 17. Igneous textures  Types of igneous textures Porphyritic texture Minerals form at different temperatures as well as differing rates Large crystals, called phenocrysts, are embedded in a matrix of smaller crystals, called the groundmass Glassy Very texture rapid cooling of molten rock Resulting rock is called obsidian
  18. 18. An obsidian flow in Oregon
  19. 19. Igneous textures  Types of igneous textures Pyroclastic texture Various fragments ejected during a violent volcanic eruption Textures often appear to more similar to sedimentary rocks Pegmatitic texture Exceptionally coarse grained Form in late stages of crystallization of granitic magmas
  20. 20. Porphyritic texture
  21. 21. Glassy texture
  22. 22. Igneous Compositions  Igneous rocks are composed primarily of silicate minerals Dark (or ferromagnesian) silicates Olivine Pyroxene Amphibole Biotite mica
  23. 23. Igneous Compositions  Igneous rocks are composed primarily of silicate minerals Light (or nonferromagnesian) silicates Quartz Muscovite Feldspars mica
  24. 24. Igneous compositions  Granitic versus basaltic compositions Granitic composition Composed of light-colored silicates Designated as being felsic (feldspar and silica) in composition Contains high amounts of silica (SiO2) Major constituents of continental crust
  25. 25. Igneous compositions  Granitic versus basaltic compositions Basaltic composition Composed of dark silicates and calcium-rich feldspar Designated as being mafic (magnesium and ferrum, for iron) in composition More dense than granitic rocks Comprise the ocean floor as well as many volcanic islands
  26. 26. Igneous compositions  Other compositional groups Intermediate (or andesitic) composition Contain at least 25 percent dark silicate minerals Associated with explosive volcanic activity Ultramafic Rare composition composition that is high in magnesium and iron Composed entirely of ferromagnesian silicates
  27. 27. Classifying Igneous Rocks  Igneous  Crystal rock textures: size is dictated by the rate of cooling of the magma body. A slower cooling rate results in larger mineral crystals being formed in the rocks as they cool.  Porphyritic texture - Large crystals surrounded by fine grained rock. The rock initially cools slowly to form some large crystals and then cools quickly to form the fine grained rock surrounding them.
  28. 28. Mineralogy of common igneous rocks
  29. 29. Igneous compositions  Silica content as an indicator of composition Silica content in crustal rocks exhibits a considerable range A low of 45 percent in ultramafic rocks Over 70 percent in felsic rocks
  30. 30. Igneous compositions  Silica content influences a magma’s behavior Granitic High magma silica content Extremely viscous Liquid exists at temperatures as low as 700oC
  31. 31. Igneous compositions  Silica content influences a magma’s behavior Basaltic Much magma lower silica content Fluid-like behavior Crystallizes at higher temperatures
  32. 32. Igneous compositions  Naming igneous rocks – granitic (felsic) rocks Granite  Phaneritic  Over 25 percent quartz, about 65 percent or more feldspar  May exhibit a porphyritic texture  Very abundant as it is often associated with mountain building  The term granite covers a wide range of mineral compositions
  33. 33. Granite
  34. 34. Igneous compositions  Naming igneous rocks – granitic (felsic) rocks Rhyolite Extrusive equivalent of granite May contain glass fragments and vesicles Aphanitic texture Less common and less voluminous than granite
  35. 35. Rhyolite
  36. 36. Igneous compositions  Naming rocks igneous rocks – granitic (felsic) Obsidian Dark colored Glassy texture Pumice Volcanic Glassy texture Frothy appearance with numerous voids
  37. 37. Obsidian
  38. 38. Pumice
  39. 39. Igneous compositions  Naming igneous rocks – intermediate rocks Andesite Volcanic origin Aphanitic texture Often resembles rhyolite
  40. 40. Andesite porphyry
  41. 41. Igneous compositions  Naming igneous rocks – intermediate rocks Diorite Plutonic equivalent of andesite Coarse grained Intrusive Composed mainly of intermediate feldspar and amphibole
  42. 42. Diorite
  43. 43. Igneous compositions  Naming igneous rocks – basaltic (mafic) rocks Basalt Volcanic origin Aphanitic texture Composed mainly of pyroxene and calciumrich plagioclase feldspar Most common extrusive igneous rock
  44. 44. Basalt
  45. 45. Igneous compositions  Naming igneous rocks – basaltic (mafic) rocks Gabbro Intrusive equivalent of basalt Phaneritic texture consisting of pyroxene and calcium-rich plagioclase Makes up a significant percentage of the oceanic crust
  46. 46. Gabbro
  47. 47. Igneous compositions  Naming igneous rocks – pyroclastic rocks Composed of fragments ejected during a volcanic eruption Varieties Tuff – ash-sized fragments Volcanic breccia – particles larger than ash
  48. 48. The Scheme for Igneous Rock Identification
  49. 49. Mineralogy of common igneous rocks
  50. 50. A Brief Tour
  51. 51. Crystal size Grain Size Description
  52. 52. Where it was formed Outside the volcano: Extrusive Inside the Earth: Intrusive
  53. 53. Bubbles ? Yes= Vesicular
  54. 54. Bubbles ? No=Non-vesicular
  55. 55. Dark Very Light NotVery Light nor Dark Very Color LightNeitherLightNot Very Dark Dark Darkest Lightest
  56. 56. Densit Very Light Medium Density Light DenseVery Dense y
  57. 57. Finding T he Miner Unless you have other information, Identify the rock als work in the middle of the rock’s box.
  58. 58. This is the amount of Potassium Feldspar in the rock.
  59. 59. This is the amount of Quartz in the rock.
  60. 60. This is the amount of Plagioclase Feldspar in the rock.
  61. 61. Use tick marks on a scrap paper to measure the percentage. Potassium Feldspar 25% Quartz 40%
  62. 62. Pr actic e Rhyolite Name a light-colored, fine-grained rock with no bubbles.
  63. 63. Name a coarse-grained, dense rock. Gabbro
  64. 64. suwun
  65. 65. Igneous rocks have “Intergrown Crystals”
  66. 66. Intergrown
  67. 67. Intergrown
  68. 68. Intergrown
  69. 69. Not Intergrown

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