Rocks and Minerals

• Minerals


  Naturally formed crystals that are composed of one or more chemical elements, distinguished from other solid natural materials by their crystalline structure, most are formed by inorganic processes though a few are formed by organic processes
• Compositions of Minerals

  • Silicates
  • Oxides
  • Sulfides
  • Sulfates
  • Halides
  • Carbonates
  • Native Metals
• Silicates


  • Silicon-oxygen tetrahedrons
• Oxides


  • Metal cations bonded to oxygen anions (ex. hematite)
• Sulfides


  • Sulfur atom bonded to oxygen atoms (ex. galena)
• Sulfates


  • Sulfur atom bonded with either a metal or non-metal element
• Halides


  • Composed of halogen ions such as chlorine and fluorine
• Carbonates


  • Presence of carbonic ion
• Native Metals


  • Consists of a native metals such as copper and gold
• Physical Properties of Minerals

  • Color
  • Crystal Form or Habit
  • Hardness
  • Streak
  • Cleavage
  • Fracture
• Color


  Most obvious property but not always definitive, can tell impurities present in the mineral, reliable for opaque and metallic minerals
• Crystal Form or Habit


  Morphology of the crystal growth, the dimensional structure of the minerals
• Hardness


  Measure of the resistance of a mineral, Friedrich Mohs' Scale of Hardness
• Streak

  Color displayed in finely powdered form left behind when rubbed on a surface, color is different when rubbed to the surface of a rock
• Cleavage


  How smooth or rough the surface is
• Fracture


  When the edges break, there is still light passing through
• Rocks


  Made up of minerals, the exception being glossy rocks, most are polymineralic (contains one or more minerals) but a few are monomineralic (ex. limestones and marble)
• Types of Rocks

  • Igneous Rocks
  • Sedimentary Rocks
  • Metamorphic Rocks
• Formation of Igneous Rocks

  Magma (molten rock found at the mantle of the Earth) cools and solidifies, can happen in the Earth's crust (intrusive igneous rocks) or on the surface (extrusive igneous rocks)
• Intrusive Igneous Rocks


  • Form when magma cools slowly at a depth, allowing the constituent minerals to grow much larger, have a coarse-grained texture
• Extrusive Igneous Rocks


  • Form when magma reaches the surface of the Earth through volcanic fissures or vents, cool rapidly and have a fine-grained or glossy texture, explosive eruption produce rock composed of rock dust
• Igneous Rock Compositions

  • Felsic Rocks
  • Mafic Rocks
  • Intermediate Rocks
• Felsic Rocks


  • Light-colored igneous rocks with high content of silica (Si02), rich in minerals like quartz, feldspar, and mica (ex. granite and rhyolite)
• Mafic Rocks


  • Dark-colored igneous rocks with a lower silica content than felsic rocks, richer in iron and magnesium and contain minerals like pyroxene and olivine (ex. basalt and gabbro)
• Intermediate Rocks


  • Fall in between felsic and mafic rocks in terms of silica content and mineral composition (ex. andesite and diorite)
• Formation of Sedimentary Rocks

  Weathering and erosion break down larger rocks into smaller pieces which are then transported by wind, water, or glaciers, these fragments settle and accumulate in layers and over time, these layers get compressed and cemented together to form the rock, minerals dissolved in water precipitate out of solution due to changes in temperature, pressure, or evaporation
• Processes of Sediment Turning into Stone

  1. Cementation

  2. Compaction

  3. Lithification
• Cementation


  Process where dissolved minerals in water precipitate (come out of solution) and fill the spaces between these sediment, minerals act like glue, binding the grains together and creating a more rigid structure
• Compaction


  As more and more sediment accumulates on top, the weight of these overlying layers presses down on the buried sediment below, this pressure squeezes the grains together, forcing out water and reducing the pore space (empty spaces) between them, increases the density and strength of the sediment, making it a more solid foundation for further transformation
• Lithification


  Entire process of transforming loose sediment into solid sedimentary rock, encompasses both compaction and cementation, along with any other chemical or physical changes the sediment undergoes during burial, loose and unconsolidated sediment becomes a hard, coherent rock with reduced pore space
• Formation of Metamorphic Rocks

  Caused by immense pressure and heat from the mantle, these extreme conditions can occur deep within the Earth's crust during subduction, near intruding hot magma, or from the immense forces exerted by tectonic plates, recrystallization occurs when the intense heat and pressure causes the minerals in the original rock (protolith) to become unstable and dissolve, forming new minerals that are more stable under the new conditions
• Types of Metamorphism

  • Dynamic Metamorphism
  • Thermal Metamorphism
• Dynamic Metamorphism


  Mechanical disruption and reorganization of the original materials within the rocks due to breaking and crushing without any appreciable chemical changes
• Thermal Metamorphism


  Causes the materials of rocks to chemically alter and re-crystallize
• Types of Thermal Metamorphism

  • Contact Metamorphism
  • Regional Metamorphism
• Contact Metamorphism


  Rocks come in contact with high-temperature intruding magma and lava, rock materials then recrystallize due to high temperature, new minerals may also form from the magma or lava that comes into contact with the rock
• Regional Metamorphism


  Occurs over a large area due to deformation caused by tectonic shearing, along with high temperature and/or pressure, do not melt as they simply transform under the intense pressure and heat
• Metamorphic Rock Textures

  • Foliation
  • Lineation
  • Banding
• Foliation


  Any layered or banded appearance in the rock due to the parallel alignment of flat or elongated materials, does not have to be strictly horizontal layers
• Lineation


  Elongated materials or grains creating a streaky or fibrous look in the rock