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sedimentary particles

Standard sieve sizes are given here.

More sophisticated than sieves is a method makes the size of an irregular particle the diameter of a spherical particle which sinks in a viscous liquid at the same speed as the irregular particle.

Geophysics employs a number of specialized classifications by particle size.

American Geophysical Union system

Name	Diameter in millimeters
small boulders	more than 256
large cobbles	128–256
small cobbles	128–64
very coarse gravel	64–32
coarse grave;	32–16
medium gravel	16–8
fine gravel	8–2
very fine gravel	4–2
very coarse sand	2–1
coarse sand	1–0.5
medium sand	0.5–0.25
fine sand	0.25–0.125
very fine sand	0.125–0.062
coarse silt	0.062–0.031
medium silt	0.031–0.062
fine silt	0.016–0.008
very fine silt	0.008–0.004
coarse clay	0.004–0.002
medium clay	0.002–0.001
fine clay	0.001–0.0005
very fine clay	less than 0.0005

Emory Wilson Lane.
Report of the subcommittee on sediment terminology.
Transactions of the American Geophysical Union, volume 28? number 6, 1947.

Wentworth system

One well-known classification of "detrital particles" was published by C. K. Wentworth in 1922.

Name	Diameter in millimeters
boulder	over 256
cobble	64 to 256
pebble	2 to 64
sand	1/16 to 2
silt	1/256 to 1/16
clay-sized particle	1/256

C. K. Wentworth.
Journal of Geology, volume 30, pages 377-392, 1922.

Udden system

A revision and extension of the Wentworth system.

Name	Diameter in millimeters
boulder	over 256
cobble	64–256
pebble	4–64
granule	2–4
very coarse sand	1–2
medium sand	0.5–1
fine sand	0.125–0.5
very fine sand	0.0625–0.125
silt	0.0039–0.0625
clay	0.00024–0.0039
colloid	less than 0.0024

Phi value

Particles are sized by the negative logarithm to the base 2 of the particle's diameter in millimeters. Users often classify particles into ½Φ classes. Some examples:

Phi scale value	Diameter, millimeters
-12Φ	4096
-8Φ	256
-6Φ	64
-3Φ	8
0Φ	1
4Φ	1/16
6Φ	1/64
8Φ	1/256

U. S. Dept. of Agriculture

Name	Diameter in millimeters
stones	over 250
cobble	250–76
gravel	76–2
very coarse sand	2–1
coarse sand	1–0.5
medium sand	0.5–0.25
fine sand	0.25–0.10
very fine sand	0.10–0.005
coarse silt	0.005–0.002
fine silt
clay	less than 0.002

USDA. 1951 Soil Survey Manual, page 208.

resources

VisualCapitalist.com has a superb graphic this link goes to another website comparing the sizes of sub-100 micrometer particles.

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