The term “clay” is applied both to Earth materials with a particle size equal to or less than 0.005 mm and to those minerals that are microcrystalline, layered, hydrous aluminum phyllosilicates, occasionally with variable amounts of iron, magnesium, and alkali metals (Gillott 1968; West 2010). Therefore, cohesive soils may be composed of mixtures of clay minerals and clay-sized materials like quartz, feldspar, and carbonate. Both clay minerals and clay-sized particles are the product of weathering from pre-existing rocks and found on or near the earth surface.