Igneous rocks 2011acloutier copyright


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Igneous Rock formed from Magma
Crystals from molten rock > silica

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Igneous rocks 2011acloutier copyright

  1. 1. Igneous Rocks by Ann C. Cloutier Earth & Space Science acloutier copyright 2011
  2. 2. Igneous rocks are formed from the crystallization of magma.  can form on or near the surface of Earth > extrusive igneous rock  or form internally beneath the Earth surface > intrusive igneous rock  granite is the most common intrusive igneous rock  ignis is Latin for “fire”  lava is magma that has flowed out onto Earth’s surface acloutier copyright 2011
  3. 3. Lava & Magma are the same except where they cool       Lava cools quickly on the surface forming fine grained crystals > tuff, scoria, pumice Ejected lava does not have time to form crystals we can see > obsidian (volcanic glass) rhyolite Magma cools slowly beneath Earth’s surface and forms larger coarse grained igneous rocks > granite pegmatites Aa and Pahoehoe are Hawaiian words geologist use for types of lava acloutier copyright 2011
  4. 4. Magma is a mix of gases, rock, water and mineral crystals  elements found in magma are the same major elements found in Earth’s crust  oxygen, silicon, aluminum, iron, magnesium, calcium, potassium , sodium  Silica is the most abundant and affects the characteristics of magma acloutier copyright 2011
  5. 5. Three types of magma  Basaltic Granitic Andesitic  magma characteristics vary due to water content and silica Si O 2 water and silica can affect the melting temperature  which will affect the magma’s viscosity  (how it flows) acloutier copyright 2011
  6. 6. How do rocks melt ?  to melt rock we need temperatures ~ 800 * C – 1,200 * C  partial melting occurs because different minerals have different melting points  magma can have a mix of molten rock and unmelted rock crystals > which explains why some crystal in magma are larger than others acloutier copyright 2011
  7. 7. Pegmatite's are cooled magma Gems often are found in pegmatites  Gems are formed under these conditions of slow cooling magma deep underground acloutier copyright 2011
  8. 8. Geothermal Gradient      affect the type of magma formed Temperature Pressure Water content Mineral composition The greater the pressure on the rock results in the higher the melting point will become. The greater the water content results in the decrease in the melting point acloutier copyright 2011
  9. 9. Where does all the heat come from ? Heat is transferred from Earth’s core > to the mantle > on to the lithosphere acloutier copyright 2011
  10. 10. Fractional Crystallization  When magma cools, it crystallizes in the reverse order of partial melting-the first minerals to crystallize from magma, are the last minerals to melt during partial melting acloutier copyright 2011
  11. 11. Bowen’s Reaction Series    Canadian geologist N.L.Bowen demonstrated that as magma cools, minerals form in predictable patterns known as Bowen’s Reaction Series (BRS) illustrates the relationship between cooling magma and the minerals that form Two main patterns were discovered and documented by Bowen: 1. a continuous pattern, with gradual changes of mineral composition in the feldspar group 2. is characterized by an abrupt change of mineral types in the iron-magnesium group discontinuous pattern acloutier copyright 2011
  12. 12. Chart with Bowen’s Reaction temperatures http:// www.youtube.com/watch?v=en6ihAM9fe8 acloutier copyright 2011 magma type
  13. 13. Igneous Rock Formation classified by light or dark minerals acloutier copyright 2011
  14. 14. Classification of Igneous Rocks acloutier copyright 2011
  15. 15. Silica content and Density acloutier copyright 2011
  16. 16. Igneous Rocks can be formed Intrusively or Extrusively  Intrusive igneous rocks form inside the Earth’s crust  Extrusively formed rocks form outside or near the surface of the Earth’s crust acloutier copyright 2011
  17. 17. Concept map of igneous rock formation acloutier copyright 2011
  18. 18. Crystal size and cooling rate    the relationship of how large a crystal can become is determined by the amount of time and space allowed for a crystal to form. small crystals cooled quickly larger crystals cooled Rare and s l o w l y beautiful acloutier copyright 2011
  19. 19. Felsic < > Mafic Rock     Felsic rock such as granite, are light-colored and have high silica content, contain quartz and the feldspars orthoclase Mafic rocks such as gabbro, are dark-colored have lower silica content and are rich in iron and magnesium Mafic rocks can contain plagioclase, biotite, amphibole, pyroxene and olivine Grain size and texture give more clues when identifying igneous rocks acloutier copyright 2011
  20. 20. Texture of Igneous Rocks     Porphyritic texture are rocks with two different grain sizes Granite is the most durable igneous rock and is used in many construction projects Granite has interlocking grain crystals which give it great strength Pegmatites have largegrained mineral crystals acloutier copyright 2011
  21. 21. Kimberlite There’s diamonds in them’ there hills or craters ! acloutier copyright 2011
  22. 22. Diamonds can be found on all continents including the USA acloutier copyright 2011
  23. 23. Ores gold, silver, copper, lead      valuable ore deposits are often associated with igneous rocks must be mined for a profit $$$$$ ores often form in the Earth when fluids left during magma crystallization contain high levels of silica and water. leftover elements that were not incorporated into common minerals important metallic elements > gold,silver,lead,copper form in metal rich veins acloutier copyright 2011
  24. 24. Mining magnetite acloutier copyright 2011
  25. 25. Most of New York’s skyscrapers were built using granite > a strong igneous rock I love the Empire State building ! The End acloutier copyright 2011