Particle size (grain size) facts for kids

Kids Encyclopedia Facts
Wentworth scale
Wentworth grain size chart from United States Geological Survey Open-File Report 2006-1195
Cobbles Nash Point
Beach cobbles at Nash Point, South Wales.

Particle size, also called grain size, means the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be used for other granular materials.

φ scale Size range
(metric)
Size range
(approx. inches)
Aggregate name
(Wentworth 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 ½–1 mm 0.020–0.039 in Coarse sand
2 to 1 ¼–½ 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 3.90625–62.5 µm 0.00015–0.0025 in Silt Mud
> 8 < 3.90625 µm < 0.00015 in Clay Mud
>10 < 1 µm < 0.000039 in Colloid Mud

In some schemes "gravel" is anything larger than sand (>2.0 mm), and includes "granule", "pebble", "cobble", and "boulder" in the above table. In this scheme, "pebble" covers the size range 4 to 64 mm (−2 to −6 φ).


Particle size (grain size) Facts for Kids. Kiddle Encyclopedia.