montmorillonite
A hydratable, dispersible claymineral of the smectite group. Montmorillonite is a three-layer, expanding clay with a large surface area and high cation-exchange capacity. Na+ and Ca+2 are the typical exchangeable cations. Sodium montmorillonite, also called sodium bentonite, is a premium clay mud additive. Natural deposits are found in Wyoming, North Dakota, South Dakota and Utah, USA. Calcium montmorillonite is a
Detailed Explanation
low-yield bentonite that is more widely distributed and used in many commercial applications, including drilling fluid.