What is a distinguishing feature of smectites in expansive soils?

Smectites are a type of clay mineral commonly found in expansive soils, and a key distinguishing feature of smectites is their highly plastic and sticky nature. This plasticity is due to the unique layered structure of smectite minerals, which allows them to absorb significant amounts of water and swell. When wet, smectite clays can expand and become quite pliable, making them capable of holding together in various forms while changing consistency. This characteristic is particularly important in construction and geotechnical contexts, as it can lead to challenges such as foundation movement or structural damage due to soil expansion and contraction.

The other options do not accurately describe smectites. The non-plastic nature would imply they do not retain water or change shape, which directly contradicts their expansive properties. High permeability is associated with soils that allow water to flow through easily, but smectites generally retain water, leading to low permeability in expansive clays. As for the identification of smectites in sandy soils, sandy soils typically do not possess significant amounts of smectite due to their coarser texture and lack of fine clay content. Thus, the choice identifying smectites as very sticky and plastic accurately reflects their distinct behavior and properties compared to other soil