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Silt is soil or rock that developed from granular material of a specific grain size.

Silty soil has much smaller particles than sandy soil, so it is smooth to the touch. When moistened, it is soapy slick. When rolled between the fingers, dirt is left on the skin.

Silty soil retains water longer, but it can’t hold on to as many nutrients as you’d want it to, though it’s fairly fertile. Due to its moisture-retentive quality, silty soil is cold and drains poorly.

Silt particles range between a 1⁄256 and 1⁄16 mm (3.9 to 62.5 μm), larger than clay but smaller than a sand. Silt is chemically distinct from clay, and unlike clay, grains of silt are about the same size in all dimensions.

Silt may occur as a soil or alternatively as suspended sediment in a water column of any surface water body. It may also exist as deposition soil at the bottom of a water body after it is eroded elsewhere and transported by a stream or by a current. Silt is easily transported in water and is fine enough to be carried long distances by air as 'dust'. Thick deposits of silty material that result from wind deposition are often called loess (a German term) or limon (French). Silt and clay contribute to more particles in the water.