SEDIMENTARY ROCKS - SLG 8.2.2

• Sedimentary Rocks - formed from pre-existing rocks and other materials such as minerals and remains of living things. These bits and pieces are called sediments.
• The word sediment came from the Latin word sedimentum which means deposit or settling. This explains the nature of the rock as these sediments settle to a location, will be compacted, and then cemented.
• There are 4 types of sedimentary rocks, namely;

  1. Detrital Sedimentary Rocks
  2. Chemical Sedimentary Rocks
  3. Biochemical Sedimentary Rocks
  4. Organic Sedimentary rocks
• Detrital sedimentary Rocks - Rocks formed from the accumulation of dead organic matter or detritus. It is mostly made up of clay minerals and quartz.
• Types of Detrital Sedimentary Rocks based on Particle Size

  1. Coarse - <2mm
  2. Medium - 1/16-2mm
  3. Fine - 1/16-1/256
  4. Very Fine - >1/256mm
• Chemical Sedimentary Rocks - formed from the materials that are carried to bodies of water like lakes & seas. The dissolved materials precipitate through physical processes to form chemical sediments.
• Biochemical Sedimentary Rocks - are formed from the remains of water-dwelling animals
• Types of Chemical and Biochemical Sedimentary Rocks

  1. Calcite, Calcium Carbonate, (CaCO3)
  2. Quartz, (Silica - SiO2)
  3. Gypsum (Calcium sulphate dihydrate CaSO4 . 2H2O)
  4. Halite(Salt–NaCl)
• Organic Sedimentary Rocks - Formed from the accumulation of organic matter and other materials in sedimentary environments. An example of this is coal.
• How are coals made? They are made for millions of years by the slow process of decay of plants and animals. The heat and pressure turned dead plants into coal.
• Distinct Features of Sedimentary Rocks

  1. Strata or beds - Layers of rocks on the Earth's surface tell stories about the past environment during the time.
  2. Fossils - these help geologists understand the environment during the time of the formation of the sedimentary rock.