What is Bentonite?

Bentonite clay is a fine-grained rock composed mainly of montmorillonite minerals. The formation of bentonite is an in situ alteration of rhyolitic volcanic ash. Pyroclastic material was ejected into the atmosphere by volcanic activity and deposited as sediment in a marine environment.

Bentonite clay is composed of microscopic platelets consisting of layers of aluminum hydroxide held between layers of silicate atoms. These platelets are stacked one on top of the other. If a gram of bentonite were spread out only one particle layer thick, its billions of particles would cover an area greater than a regulation football field.

There are two basic types of bentonite, sodium type and calcium type.

• Sodium Type - This type has sodium in the crystal lattice and is sometimes referred to as Wyoming Bentonite. This type swells when wet and can increase as much as fifteen times its original volume when wet. Wyoming bentonite occurs in the Big Horn Basin, the Powder River Basin and along the western edge of the Black Hills. Because of this unique characteristic, Wyoming Bentonite is used as the standard against all other bentonite in the world is measured.
• Calcium Type - This type has calcium in the crystal lattice and is sometimes referred to as Southern Bentonite. This type will swell only 2 times their unwetted volume. Southern Bentonite occurs in Mississippi, Arizona and other southern locations.

Its color ranges from white to black and includes shades of gray, light olive green, cream, yellow, earthy red, brown, sky blue and purple. Bentonite feels and appears greasy or waxy and when wet it is highly plastic and slippery.