Classification of Sedimentary Rocks

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  • Classification of Sedimentary Rocks
    • Breccia
      • Coarse Grains
      • Clastic (composed of pre-existing minerals and rocks)
      • Angular
      • Some finer grains set in a matrix
      • Poorly Sorted
      • Commonly formed as scree/alluvial fans
      • Volcanic breccia are pyroclastics from an eruption
    • Conglomerate
      • Coarse grains
      • Clastic (composed of pre-existing rocks and minerals)
      • Rounded (transported for longer)
      • Finer grained matrix
      • Poorly sorted
      • Commonly formed in beach or river channel
    • Sandstones
      • Main rock for oil reservoirs and aquifers of water
      • Building stones
      • Well cemented - low porosity
      • poorly cemented - high porosity
      • quartz is the main component
      • Mica, muscovite, k feldspar are common
      • Found in all sedimentary environments
    • Orthoquartzite
      • A type of sandstone
      • Only quartz grains in a quartz cement
      • Well sorted
      • Well rounded (transported for longer)
      • Less stable minerals not present - well weathered
      • Common in beach or shallow marine deposits
    • Desert Sandstone
      • Not fully quartz, iron oxide coats the grains
      • Very well sorted
      • Very well rounded
      • 1mm grains
      • Red in colour
      • Class cemented by silica or iron minerals
      • Form in arid environments as wind blown sands
    • Arkose
      • Medium to coarse grained
      • At least 25% potassium feldspar
      • Moderately sorted
      • Sub angular to sub rounded grains (not transported far)
      • Commonly formed in alluvial fan environments in arid areas
    • Greywacke
      • Fine to coarse grains
      • Dark colour
      • Poorly sorted
      • Angular to sub angular
      • Mainly rock fragments (lithic clasts)
      • >15%of the rock is clay matrix
      • Commonly formed as turbidite deposits - often show graded bedding


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