The term Bentonite was first used for a plastic clay found in about 1890 in upper cretaceous tuff near Fort Benton, Wyoming. The main constituent, which is the determinant factor  in  the  clay’s  properties,  is  the  clay  mineral montmorillonite. This in turn, derives its name from a deposit at Montmorillon, in Southern France.
Bentonite is a plastic clay generated frequently from the alteration of volcanic ash, consisting predominantly of smectite minerals, usually montmorillonite.

Depending  on  the  nature  of  their  genesis,  bentonites contain a variety of accessory minerals in addition to montmorillonite.  These  minerals  may  include  quartz , feldspar, calcite  and  gypsum.  The  presence  of  these minerals could impact the industrial value of the deposit, reducing  or  increasing  its  value  depending  on  the application.
Bentonite  presents  strong  colloidal  proper ties  and  its volume increases several times when coming into contact with water, creating a gelatinous and viscous fluid. The special properties of bentonite (hydration, swelling, water absorption, viscosity, thixotropy) make it a valuable material for a wide range of uses and applications.

Bentonite deposits are normally exploited by quarrying. Extracted bentonite is distinctly solid, even with a moisture content of approximately 30%. The material is initially crushed and, if necessary, activated with the addition of soda  ash  (Na2C O3).  Bentonite  is  subsequently  dried  (air and/or forced drying) to reach a moisture content of approximately 15%. According to the final application, bentonite is either sieved (granular form) or milled (into powder  and  super fine  powder  form).  For  special applications,  bentonite  is  purified  by  removing  the associated  gangue  minerals,  or  treated  with  acids  to produce acid activated bentonite (bleaching earths), or treated with organics to produce organoclays.