Silt

Silt is a sedimentary material composed of fine particles with a grain size between about 0.0039 and 0.0625 millimeters, roughly 4 to 62.5 micrometers. On the Wentworth scale, it lies between sand and clay. In practice, some sources extend the lower limit to around 2 micrometers.

Most silt consists of tiny fragments of minerals such as quartz, feldspar, and mica, and may include organic matter. It forms by weathering and disintegration of rocks, and is transported by rivers, wind, or glaciers, eventually settling in quiet waters where the flow loses energy.

Physically, silt grains are smooth and often appear powdery when dry. They have little cohesion when dry, but can become sticky and plastic when wet. Silt soils offer higher water-holding capacity than sandy soils but drain more quickly than clay, and they tend to compact under load.

Geographically, silt is common in river floodplains, lake beds, deltas, and in wind-blown deposits known as loess. Sediment layers of silt record past climates and hydrological conditions.

Uses and limitations: In agriculture, silt-rich soils (silt or silt loam) are valued for fertility and workability but can suffer from erosion and poor structure when wet. In construction, silt is generally unsuitable as a primary aggregate due to low strength.

Environmental and hydrological significance: Silt can carry pollutants in suspension and contribute to sedimentation in reservoirs, waterways, and estuaries. Management of erosion and sediment transport is important to maintain water quality.