Bentonite is a very peculiar type of clay which is the disintegration product of glassy particles of volcanic ash. Chemically, bentonites contain more silica, lime and magnesia than Ball clay. But the alumina content is very low while iron content is very high than that of ball clays and china clays. The colour of bentonite varies from pearl cream to buff grey, pink or sometimes yellow. The texture is compressed and hard, when we soak it in water it swells and crumbles and the liquid suspension remains permanant.
There are two major classifications of Bentonite - calcium bentonite and magnesium bentonite. The water content (chemical) is very high compared to other kaolinite clays. Bentonite is used as a substitute for plastic clay in the ceramic, pencil and crayon industries. It is also used in some pharmaceutical and cosmetic preparations. It is used as a suspending agent for pottery glazes and enamels, for de watering and clarifying petrolium and other oils and as a flocculating material in drilling applications. It is used as a mordant in the dye industry and as a base for lake colours. It is also used as a bonding material in foundry work.
