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;
Detrital Sedimentary Rocks
Chemical Sedimentary Rocks
Biochemical Sedimentary Rocks
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
Coarse - <2mm
Medium - 1/16-2mm
Fine - 1/16-1/256
VeryFine - >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
Calcite, Calcium Carbonate, (CaCO3)
Quartz, (Silica - SiO2)
Gypsum (Calcium sulphate dihydrate CaSO4 . 2H2O)
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 deadplants into coal.
Distinct Features of Sedimentary Rocks
Strata or beds - Layers of rocks on the Earth's surface tell stories about the past environment during the time.
Fossils - these help geologists understand the environment during the time of the formation of the sedimentary rock.