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The Udden-Wentworth scale is a geometric scale of grain sizes which classifies particles of siliciclastic sediment from 4096 millimeters (boulders) in size down to 0.00006 millimeters (clay). This scale is almost universally accepted by modern sedimentologists (a type of geologist who studies sedimentary rocks).

Particle sizes:

  • cobbles: 64-246 mm
  • pebbles: 4-64 mm
  • granules: 2-4 mm
  • very coarse sand: 1-2 mm
  • coarse sand: 0.5-1 mm
  • medium sand: 0.25-0.5 mm
  • fine sand: 0.125-0.25 mm
  • very fine sand: 0.0625-0.125 mm
  • silt: 0.0039 - 0.0625 mm
  • clays: 0.00006 - 0.0039 mm

It was first proposed in 1898 by J.A. Udden and then modified and extended in 1922 by Wentworth.


From the science dictionary at http://biotech.icmb.utexas.edu/

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