The Rock Cycle

by Ryan McCarty and Gregory Turner

Igneous, sedimentary, and metamorphic rocks all have important roles in a system called the rock cycle. Each rock can be altered to become any other kind of rock.


Igneous Rocks

  • igneous rocks are rocks formed from the crystallization of magma
  • crystallization
    • the process in which atoms become minerals or minerals become other minerals
    • takes place when magma cools or when a substance is dissolved in water and then cools
  • magma
    • a mixture of molten or semi-molten rock beneath Earth’s surface
  • lava
    • hot molten or semi-fluid rock above Earth's surface erupted from a volcano or fissure
  • intrusive
    • igneous rock formed slowly beneath Earth’s surface
    • coarse grained
  • extrusive
    • igneous rocks formed quickly above Earth’s surface
    • fine grained
  • felsic/granitic (for example: granite)
    • contains a high percentage of silicate minerals
    • light-colored
    • not very dense
    • intrusive
    • coarse grained
  • intermediate/andesitic (for example: andesite)
    • grey-colored
    • medium-sized crystals
  • mafic/basaltic (for example: basalt)
    • in modern times, basalt is commonly used as aggregates, constructing purposes, sculpting purposes, and flooring coverings and veneers
    • contains a low percentage of silicate minerals
    • dark-colored
    • dense
    • extrusive
    • fine grained
  • coarse grained
    • intrusive
    • big crystals
    • has time to bond with its surroundings which results in large crystals
  • fine grained
    • extrusive
    • small crystals
    • does not have time to bond with its surroundings which results in small crystals
  • porphyritic
    • large crystals or grains embedded in a matrix of smaller crystals or grains
    • this texture exists when a rock has two cooling rates
  • minerals
    • a naturally occurring, inorganic solid that has a crystal shape and a definite chemical composition
    • formed through crystallization or evaporation
  • silicates
    • rock forming minerals

Sedimentary Rocks

  • sedimentary rocks are rocks formed from the compaction and cementing of loose particles of sediment, evaporation of a solution, or precipitation of loose particles of sediment
  • weathering
    • caused by wind and rain
  • erosion
    • happens when loose particles of rocks and minerals are eroded due to weathering
  • deposition
    • happens when the eroded particles are transported downstream
    • heaviest sediment is deposited first
      • first: gravel
      • second: sand
      • third: silt
      • fourth: clay
      • fifth: mud particles
  • compaction
    • pressure from different layers
  • cementing
    • when pressure is applied, water leaves and cementing minerals are left behind
  • transportation
    • happens when loose particles of sediment is moved downstream
  • clastic (for example: breccia)
    • in modern times, breccia is used as decoration of walls and floors and is used as an aggregate
    • formed from the compaction and cementing of eroded debris
  • chemical (for example: chemical limestone)
    • formed through evaporation and precipitation
  • organic (for example: organic limestone)
    • formed from the compaction and cementing of debris containing fossils


Metamorphic Rocks

  • metamorphic rocks are rocks formed from heat and pressure applied to any classification of rock
  • contact metamorphism
    • metamorphism in which heat from a magma chamber is applied over a small area
  • regional metamorphism
    • metamorphism in which pressure from the movement of tectonic plates is applied over a large area
  • foliated (for example: gneiss)
    • in modern times, gneiss is used as a building material for flooring, ornamental stones, gravestones, facing stones on buildings, and work surfaces
    • mineral crystals are arranged in parallel layers or bands
  • non-foliated (for example: quartzite)
    • mineral crystals are not organized in parallel layers or bands
    • do not break into layers
  • parent rock
    • all metamorphic rocks have a parent rock
    • the parent rocks are the original rocks before metamorphism
    • for example, granite is the parent rock of gneiss and shale is the parent rock of slate
  • recrystallization
    • changes the appearance/texture, crystal structure, or mineral composition of a rock

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