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Sediment facts for kids

Kids Encyclopedia Facts
Cobbles Nash Point
Cobbles on a beach
Leman img 0573
River Rhône flowing into Lake Geneva. Sediments make the water appear brownish-grey; they are an indicator of increased water runoff, land degradation, erosion due to intensive industrialized land use, land sealing, and poor soil management.

Sediment is the matter which falls to the bottom of oceans and lakes. Compressed and gradually transformed, sediment is the basis of sedimentary rocks. The term is also used for material transported by wind or water, and deposited on the surface. In due course, this may also turn into rock. The study of how sedimentary rocks are formed is called sedimentology.

In more general use, sediment is any matter which falls to the bottom of a liquid, such as juice.


Sediment in the Gulf of Mexico
Sediment in the Gulf of Mexico
Sediment off the Yucatan Peninsula
Sediment off the Yucatán Peninsula

Sediment can be classified based on its grain size or composition.

Grain size

Sediment size is measured on a log base 2 scale, called the "Phi" scale, which classifies particles by size from "colloid" to "boulder".

φ scale Size range
Size range
Aggregate class
Other names
< -8 > 256 mm > 10.1 in Boulder
-6 to -8 64–256 mm 2.5–10.1 in Cobble
-5 to -6 32–64 mm 1.26–2.5 in Very coarse gravel Pebble
-4 to -5 16–32 mm 0.63–1.26 in Coarse gravel Pebble
-3 to -4 8–16 mm 0.31–0.63 in Medium gravel Pebble
-2 to -3 4–8 mm 0.157–0.31 in Fine gravel Pebble
-1 to -2 2–4 mm 0.079–0.157 in Very fine gravel Granule
0 to -1 1–2 mm 0.039–0.079 in Very coarse sand
1 to 0 0.5–1 mm 0.020–0.039 in Coarse sand
2 to 1 0.25–0.5 mm 0.010–0.020 in Medium sand
3 to 2 125–250 μm 0.0049–0.010 in Fine sand
4 to 3 62.5–125 μm 0.0025–0.0049 in Very fine sand
8 to 4 3.9–62.5 μm 0.00015–0.0025 in Silt Mud
> 8 < 3.9 μm < 0.00015 in Clay Mud
>10 < 1 μm < 0.000039 in Colloid Mud


Composition of sediment can be measured in terms of:

This leads to an ambiguity in which clay can be used as both a size-range and a composition (see clay minerals).

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Sediment Facts for Kids. Kiddle Encyclopedia.