Bentonite is a crystalline, claylike mineral, and is available as an odorless, pale buff, or cream to grayish-colored fine powder, which is free from grit. It consists of particles about 50–150 mm in size along with numerous particles about 1–2 mm. Microscopic examination of samples stained with alcoholic methylene blue solution reveals strongly stained blue particles. Bentonite may have a slight earthy taste.
Albagel; bentonitum; E558; mineral soap; Polargel; soap clay; taylorite; Veegum HS; wilkinite.

Nonproprietary Names

BP: Bentonite
JP: Bentonite
PhEur: Bentonite
USP-NF: Bentonite

Albagel; bentonitum; E558; mineral soap; Polargel; soap clay; taylorite; Veegum HS; wilkinite.

Chemical Name and CAS Registry Number

Bentonite [1302-78-9]
Empirical Formula and Molecular Weight
Al2O3_4SiO2_H2O 359.16
Bentonite is a native colloidal hydrated aluminum silicate consisting mainly of montmorillonite, Al2O3_4SiO2_H2O; it may also contain calcium, magnesium, and iron. The average chemical analysis is expressed as oxides, see Table I, in comparison with magnesium aluminum silicate.

Structural Formula

The PhEur 6.4 describes bentonite as a natural clay containing a high proportion of montmorillonite, a native hydrated aluminum silicate in which some aluminum and silicon atoms may be replaced by other atoms such as magnesium and iron.
The USP32–NF27 describes bentonite, purified benonite, and bentonite magma in three separate monographs. Bentonite is described as a native, colloidal, hydrated aluminum silicate; and purified bentonite is described as a colloidal montmorillonite that has been processed to remove grit and nonswellable ore compounds.

Functional Category

Adsorbent; stabilizing agent; suspending agent; viscosity increasing agent

Applications in Pharmaceutical Formulation or Technology

Bentonite is a naturally occurring hydrated aluminum silicate used primarily in the formulation of suspensions, gels, and sols, for topical pharmaceutical applications. It is also used to suspend powders in aqueous preparations and to prepare cream bases containing oil-in-water emulsifying agents.

Bentonite may also be used in oral pharmaceutical preparations, cosmetics, and food products. In oral preparations, bentonite, and other similar silicate clays, can be used to adsorb cationic drugs and so retard their release. Adsorbents are also used to mask the taste of certain drugs.

Bentonite has been investigated as a diagnostic agent for magnetic resonance imaging. Therapeutically, bentonite has been investigated as an adsorbent for lithium poisoning.

Method of Manufacture

Bentonite is a native, colloidal, hydrated aluminum silicate, found in regions of Canada and the USA. The mined ore is processed to remove grit and nonswelling materials so that it is suitable for pharmaceutical applications.