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Igneous Rocks & Rock Structures

Igneous Rocks & Rock Structures. These notes go on pp. 7 & 9 of your Igneous rock INB!!!. Igneous rocks are formed by the crystallization of molten rock ( lava or magma ). Classification. Mineral Composition Texture of Grain Size. Mineral Composition.

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Igneous Rocks & Rock Structures

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  1. Igneous Rocks & Rock Structures These notes go on pp. 7 & 9 of your Igneous rock INB!!!

  2. Igneous rocks are formed by the crystallization of molten rock (lava or magma).

  3. Classification • Mineral Composition • Texture of Grain Size

  4. Mineral Composition

  5. Felsic: high amounts of silica & light in color

  6. Felsic Rocks and Minerals

  7. Mafic: low amounts of silica & dark in color

  8. Mafic Rocks

  9. Silica Composition Felsic rocks - more than 65% silica content Intermediate rocks - 50-65% silica content (also called andesitic) Mafic rocks - less than 40-50% silica

  10. Pure Silica

  11. Texture of Grain Size

  12. 1. Igneous rocks formed above ground from lava are called “Extrusive” or “Volcanic” rocks. Obsidian Rhyolite

  13. cools rapidlyand crystals have a limited time to form; as a result there are small or no mineral crystals

  14. Resulting Textures: • Glassy • Porous/Vesicular • Fine-Grained

  15. Obsidian-Glassy Felsic

  16. Scoria-Vesicular Mafic

  17. 2. Igneous rocks formed underground from Magma are called Plutonic or Intrusive rocks. Notice the large crystals

  18. cools slowly and large crystals have time to form.

  19. Resulting Textures 1. Coarse Grained

  20. Granite- Coarse-grained Felsic

  21. Gabbro- Coarse-grained Mafic

  22. Igneous rocks that begin to cool underground and then are erupted to the surface have both fine and coarse grains. These rocks have undergone two stages of cooling, therefore they have two sizes of crystals. These rocks have porphyritic texture.

  23. Basalt Porphyry- Mafic

  24. Rhyolite Porphyry-Felsic

  25. Igneous Rock Structures These notes go on p. 9 of your INB!!!

  26. Intrusive Igneous Rock formations:

  27. Dikes Dike: Sheet-like Igneous rocks that cut acrossthe structure of pre-existing rock.

  28. Dike

  29. Sills Sills: Sheet-like Igneous rock that lies parallel to the layering of pre-existing rock.

  30. Sill

  31. Laccoliths Laccoliths: verticallydeveloped sills.

  32. Batholiths Batholiths: a large Plutonic mass of Igneous Rock. Usually makes up the core of volcanicmountains

  33. Halfdome- Yosemite, California

  34. Enchanted Rock-Texas

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