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• How igneous rocks are formed

  Magma or lava (hot melted rock materials) cools and hardens
• Magma


  Molten rock material mostly formed in the Earth's mantle
• Lava


  Magma that reaches the surface
• Extrusive igneous rocks


  • Cool quickly, fine grained or lack crystal growth
• Intrusive igneous rocks


  • Cool slowly, coarse grained
• Most abundant elements in igneous rocks

  • Silicon
  • Oxygen
  • Aluminum
  • Calcium
  • Sodium
  • Potassium
  • Magnesium
  • Iron
• Silicate


  Compound of 1 silicon and 4 oxygen atoms
• Silicate minerals


  • Feldspar
  • Mica
  • Olivine
  • Quartz
  • Pyroxene
• Dark silicate materials


  • Rich in iron and/or magnesium, low in silica
• Light silicate materials


  • Rich in potassium, sodium, calcium, rich in silica
• Light silicate minerals


  • Feldspar
  • Quartz
  • Muscovite
• Four main types of igneous rocks

  • Granitic (felsic)
  • Basaltic (mafic)
  • Andesite (intermediate)
  • Ultramafic
• Granitic (felsic) igneous rocks

  • Derived from feldspar and silica-quartz, mostly found in continental crust
• Felsic igneous rocks


  • Granite
  • Rhyolite
• Basaltic (mafic) igneous rocks


  • Darker and denser, rich in magnesium and iron, mostly found in oceanic crust
• Mafic igneous rocks


  • Basalt
  • Obsidian
  • Gabbro
• Andesite (intermediate) igneous rocks

  • Contain at least 25% dark silicate minerals (amphibole, pyroxene, biotite mica) plus plagioclase and feldspar
• Andesite igneous rocks


  • Andesite
  • Diorite
• Ultramafic igneous rocks


  • Mostly composed of olivine and pyroxene, main component of Earth's upper mantle
• Ultramafic igneous rocks


  • Peridotite
• Types of igneous rocks based on texture

  • Fine-grained
  • Coarse-grained
  • Porphyritic
  • Vesicular
  • Glassy
  • Pyroclastic
• Fine-grained igneous rocks


  • Crystals too small to see with the naked eye, light/intermediate/dark in color, formed by very fast cooling
• Coarse-grained igneous rocks


  • Consist of large, intergrown crystals visible to the naked eye, formed by slow cooling at great depth
• Porphyritic igneous rocks


  • Large crystals (phenocrysts) embedded in a groundmass of smaller crystals, formed by different cooling rates
• Vesicular igneous rocks


  • Contain spherical voids (vesicles) from gas bubbles escaping as lava solidifies, often in upper lava flows
• Glassy igneous rocks


  • Smooth, shiny texture like glass, formed when volcanic material cools extremely quickly
• Pyroclastic igneous rocks


  • Formed from fragments of rock ejected during explosive volcanic eruptions
• Types of sedimentary rocks

  • Detrital (coarse-grained)
  • Detrital (fine-grained)
  • Chemical
  • Biochemical
• Detrital sedimentary rocks


  Formed from fragments of weathered rocks
• Chemical and biochemical sedimentary rocks

  Formed from dissolved materials precipitating or from remains of water-dwelling organisms
• Calcite


  Essential component of limestone and chalk
• Chalk


  • Calcium carbonate
  • Calcium sulfate (pastel chalks)
• Coal formation


  Dead plants buried under water and dirt, heat and pressure turned into coal over millions of years
• Types of coal


  • Peat
  • Lignite
  • Bituminous
  • Anthracite
• Some sedimentary rocks contain fossils, which help geologists understand the environment at the time of formation
• Metamorphic rocks


  Formed from pre-existing igneous, sedimentary, or metamorphic parent rocks
• Metamorphism


  Change in the form or structure of a rock due to heat, pressure, and chemical processes
• Low-grade metamorphism


  Shale -> Slate (tightly packed, chlorite and mica minerals)
• High-grade metamorphism


  Granodiorite -> Folded Gneiss (deformed layers of segregated minerals)
• Contact metamorphism


  Occurs when magma comes into contact with pre-existing rock, raising the temperature