The term clay has a double meaning and therefore should be defined when it is used. Clay is used both as a rock term and as a particle size term. As a rock term, clay is used for a natural, earthy, fine-grained material composed largely of a limited group of crystalline minerals known as the clay minerals. As a particle size term, clay is used for the category that includes the smallest particles. Soil investigators and mineralogists generally use 2Âµm as the maximum size, although the went worth scale defines clay as material finer than 4Âµm. Grim uses the term clay material for any fine-grained, natural, earthy, argillaceous material. In this way, the term can include clays, shales, or argillites and some soils if they are argillaceous. Clay are comprised of certain groups of hydrous aluminium, magnesium and iron silicates that may contain sodium, calcium, potassium, and other ions. These silicates are called the clay minerals and the major clay mineral groups are kaolins, smectites, illites, chlorites and hormites. Clay and clay minerals are important geologically, industrially and agriculturally. They are important to the engineer in building foundations, tunnels, road cuts and fills and dams. Feldspar have a vitreous to pearly luster, the colours ranging through white, cream, pink, buff brown, red, grey, green and bluish, they may be clear or milky. The fracture is uneven. More than seven industries in organized sector are engaged in the manufacturing of calcined non plastic clays. There is bright future for new entrepreneurs.