What is the smallest particle size in soil classifications?

The classification of soil based on particle size is fundamental for understanding its properties and behavior. Fines refer to the smallest particle sizes in soil, which include both clay and silt. Among these, clay particles are the finest, but the term "fines" encompasses both clay and silt as a combined category.

When discussing soil classifications, particles larger than fines fall into categories such as sand or gravel, which are considerably coarser. This distinction illustrates that "fines" as a term is correct in identifying the smallest particle size classification, as it includes all particles smaller than sand. Thus, this choice accurately represents the smallest category in the classification system.