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Igneous Rocks

Igneous Rocks. http://www.soest.hawaii.edu/coasts/lecture/gg101/index.html. What is Igneous Rock?. Earth’s crust is 4/5 igneous rock. Every igneous rock begins life as molten magma deep in the mantle. As magma migrates toward the surface, some of it chills and hardens

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Igneous Rocks

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  1. Igneous Rocks http://www.soest.hawaii.edu/coasts/lecture/gg101/index.html

  2. What is Igneous Rock? Earth’s crust is 4/5 igneous rock. Every igneous rock begins life as molten magma deep in the mantle. As magma migrates toward the surface, some of it chills and hardens underground into granite and other types of igneous rocks. Magma that makes it to the surface erupts in either flowing or explosive volcanoes, generating lava, geysers, and hot springs.

  3. Igneous rock crystallizes in Earth’s magma locations Intrusive igneous rock crystallizes within Earth’s crust. Extrusive igneous rock crystallizes upon Earth’s crust.

  4. Extrusive igneous rock Intrusive igneous rock

  5. Igneous Rocks • Igneous Rocks are named on the basis of their texture and composition. Composition of a rock is the assemblage of minerals it contains. Texture of a rock is the size and arrangement of the minerals it contains.

  6. As magma crystallizes a network of interlocking minerals develops. The composition and texture of the resulting rock is determined by these minerals.

  7. Texture Phaneritic texture - with large minerals (Granite) Large crystals had a long time to crystallize. Therefore, this is an intrusive rock

  8. Texture Aphanitic texture - mineral grains too small to see with the unaided eye (Basalt) Small crystals had a short time to crystallize. Therefore, this is an extrusive rock

  9. Texture Glassy texture - without obvious minerals (Obsidian) No crystals. This is an extrusive rock.

  10. Texture Vesicular texture – many pits from gas escape (Basalt) Extrusive rock.

  11. Texture Porphry texture – with 2 distinct grain sizes, large and small (Andesite Porphyry) What is the cooling history?

  12. Composition Igneous color (gray scale) is used to estimate chemical composition Felsic Intermediate Mafic Low Fe/Mg content…………………………………………High Fe/Mg content High Si/O content……………………………………………Low Si/O content

  13. Remember, partial melting produces magma that is enriched in Silicon and Oxygen and depleted in Iron and Magnesium

  14. Composition Felsic – oxygen, silicon, sodium enriched iron, magnesium, calcium depleted Source – partial melting, continental crust Granite - pink is considered felsic Intermediate Diorite Mafic - iron, magnesium, calcium enriched oxygen, silicon, sodium depleted Basalt Source – mantle, oceanic crust Ultramafic Dunite

  15. Composition How do igneous rocks form in a cooling magma chamber? Remember partial melting? Silica (felsic) compounds melt first – therefore in a cooling magma chamber they must crystallize last Iron-rich (mafic) compounds melt last – therefore in a cooling magma chamber they must crystallize first first Mafic – Fe/Mg/Ca last Mafic – Fe/Mg/Ca Crystallizing Melting first Felsic – Si/O/Na last Felsic – Si/O/Na Therefore a cooling magma chamber will become enriched in Si/O as it crystallizes

  16. Plagioclase Feldspar (Ca/Na) Olivine Igneous Rock-Forming Minerals Pyroxene Orthoclase Feldspar Mafic Minerals Felsic Minerals Amphibole Muscovite Mica Biotite Mica Quartz

  17. How do igneous rocks form? Bowen’s Reaction Series Types of Rocks formed Hot Ultramafic Basalt Gabbro Andesite Diorite Rhyolite Granite Ca - plagioclase Olivine Mafic Pyroxene Plagioclase feldspar Intermediate Amphibole Biotite Na - plagioclase Felsic Orthoclase feldspar Muscovite Cool Quartz

  18. The Igneous Minerals Intrusive Extrusive Granite Diorite Gabbro plutonic The Igneous Rocks Texture Rhyolite Andesite Basalt volcanic Felsic Intermediate Mafic Composition

  19. Where do the Igneous Rocks form? Intrusive Extrusive Granite Diorite Gabbro Rhyolite Andesite Basalt Felsic Intermediate Mafic

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