The distinction between silt and clay varies by discipline. Geologists and soil scientists usually consider the separation to occur at a particle size of 2 μm (clays being finer than silts), sedimentologists often use 4–5 μm, and colloid chemists use 1 μm. Geotechnical engineers distinguish between silts and clays based on the plasticity properties of the soil, as measured by the soils' Atterberg limits. ISO 14688 grades clay particles as being smaller than 2 μm and silt particles as being larger. Mixtures of sand, silt and less than 40% clay are called loam.

particle of clay

A particle which 1) is composed primarily of hydrous aluminium phyllosilicate minerals, in turn composed of aluminium and silicon ions bonded into tiny, thin plates by interconnecting oxygen and hydroxide ions, and 2) is or was part of a portion of clay.

clay particle