Silt

Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. You can find it as soil mixed with sand or clay, or as sediment in water. When dry, silt feels like flour and does not change shape when wet.

Silt is part of average modern mud. It is common in river deltas and in places like central Asia, north China, and North America. It forms from processes such as dust storms and glacial grinding.

Loess, soil rich in silt, helps create fertile land for farming. But silt can be easily moved by wind or water, which can cause problems for building. Poor farming can make pollution from silt worse.

Description

Silt is made from tiny pieces of weathered and eroded rock. It is smaller than sand but bigger than clay minerals. Most silt particles are broken pieces of quartz. When dry, silt feels floury. When wet, it does not stick together like clay does.

Scientists measure silt by its size, which is usually between very small pieces you can barely see. Different groups, like the USDA and the ISSS, have slightly different size ranges for what they call silt. But all agree that silt is gritty and not smooth like clay.

Occurrence

Silt is a very common material. It is often found where rivers spread out, such as the Nile and Niger River deltas. You can also find it in places like Bangladesh, northern China, central Asia, and North America. Silt is less common in tropical regions.

In rivers, silt can float in the water. It is also found in types of rock called mudrock. When silt makes up most of a sedimentary rock, it is called a siltstone.