Grain size

Grain size is a measure of the dimensions of individual sediment particles. It helps classify sediment and interpret how particles were transported and deposited.

Particle-size distribution: A description of the range and relative proportions of particle sizes in a material. Grain size describes individual particles; distributions summarize sizes across a sediment sample.
Stokes' law: A relation describing the drag force on a small sphere moving slowly through a viscous fluid. It helps explain why small grains settle more slowly than larger grains in water.
Grain-size analysis: The measurement of particle sizes and their proportions in a sample. It turns the general property of grain size into a reproducible sample description.
Clay: Fine-grained sediment composed of particles smaller than about 0.004 millimeters on the Wentworth scale. Clay occupies the finest end of the standard sediment-size classification.
Sediment: Loose mineral or organic particles transported and deposited by water, wind, ice, or gravity. Grain size is one of the basic properties used to describe sediment.
Settling velocity: The steady speed at which a particle falls through a fluid under gravity. Grain size strongly influences how quickly sediment particles settle.
Sieve analysis: A method that separates particles by passing a sample through stacked sieves with decreasing openings. Sieves measure the sizes of coarse sediment grains.
Silt: Fine sediment with particle diameters between about 0.004 and 0.0625 millimeters on the Wentworth scale. Silt is a distinct fine-grained class between clay and sand.
Wentworth scale: A logarithmic classification system that assigns sediment particles to size classes. It gives standard names and size boundaries for sediment grains.
Hjulström curve: A graph relating water-flow velocity to the erosion, transport, and deposition of sediment grains. It shows how grain size changes the flow needed to erode or deposit sediment.

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