Grain size Grain size Grain size (or particle size) is the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which refers to the size of a single crystal inside a particle or grain. A single grain can be composed of several crystals. Granular material can range from very small colloidal particles, through clay, silt, sand, gravel, and cobbles, to boulders. Size ranges define limits of classes that are given names in the Wentworth scale (or Udden–Wentworth scale) used in the
Silt out zero visibility. Always using guidelines during penetration dives is an important safety measure as it helps divers find their way out. Surface supplied divers are generally at less risk from silt out as they are connected to the surface by an umbilical and can not get lost, but they may become disorientated, and unable to work effectively. It is also more likely for them to have an umbilical snag in bad visibility, and if assistance is required from the stand-by diver, this is more difficult in a silt out. A severe silt out will make the video cameras on a