- DEPOSITION:
The settling of particles out of water or wind or ice is called deposition.
This includes both solid (suspended) particles and also chemical deposition of materials precipitated out of solution.
In general, the slowing down of water or wind movement results in greater deposition of sediment. So does a decrease in turbulence (a more laminar flow).
- SEDIMENTS:
Sediments are the unconsolidated (loose) materials resulting from deposition.
Sediments can be classified by origin, by size, by shape, by chemical composition, or by sorting.
- By origin: Clastic sediments are derived from the breaking up of larger fragments (Greek klastos='breaking').
Chemical precipitates are deposited by chemical processes.
Biological precipitates are the remains of shelly organisms, deposited on the sea (or lake) bottom.
- By size: Boulders are generally larger than 10 cm across.
Pebbles are particles between 0.5 and 10 cm across.
Sand is made of particles between 0.05 and 0.5 cm (or 0.5 to 5 mm) across.
Silt is made of particles between 0.05 and 0.5 mm across.
Mud is sediment made of clay size particles, smaller than 0.05 mm across. Often they are flat.
- By shape: Some sedimentary particles are well-worn and rounded; others are angular.
- By composition: Pebbles and boulders are often rock materials of mixed (heterogeneous) composition.
Sand and silt are usually mostly made of silicon dioxide (quartz, SiO2).
Clay particles are usually made of clay minerals derived from the chemical weathering of mica. Many of these minerals form flat,
flaky shapes, and many of them are hydrated (they contain water) and slippery as a result.
- By sorting: Sediments are poorly sorted if they contain a mixture of sizes and materials.
Sediments are well sorted (e.g., by back-and-forth wave action over time) if they are uniform in size and contain only one type of material.
|