ABSTRACT
Soils are aggregates of mineral particles; and together with air and/or water in the void spaces, they form three-phase systems. A naturally occurring soil sample may have particles of various sizes. Over the years, various agencies have tried to develop the size limits of gravel, sand, silt, and clay. Clay minerals are complex silicates of aluminum, magnesium, and iron. Two basic crystalline units form the clay minerals: a silicon–oxygen tetrahedron, and an aluminum or magnesium octahedron. Some clay minerals consist of repeating layers of two-layer sheets. A two-layer sheet is a combination of a silica sheet with a gibbsite sheet, or a combination of a silica sheet with a brucite sheet. The presence of clay minerals in a fine-grained soil will allow it to be remolded in the presence of some moisture without crumbling. If clay slurry is dried, the moisture content will gradually decrease, and the slurry will pass from a liquid state to a plastic state.
