What Is Bentonite?

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  • Written By: Karize Uy
  • Edited By: Lauren Fritsky
  • Last Modified Date: 12 October 2019
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Bentonite is a geological clay material that is mainly made up of a mineral group called montmorillonite. It is usually created from volcanic ash that has been disintegrated by water. Other minerals included in bentonite clay are aluminum, calcium, potassium, and sodium. The predominance of one of these minerals dictates the names of the variants. The two most common variants of bentonite are calcium and sodium. This type of material has so many uses that it has garnered the nickname “the clay of 1,000 uses.”

Geologists have estimated that the formation of bentonite can be traced as far back as 70 million years. This means that the clay has settled in the lower layers of the earth’s soil and usually requires mining and quarries to be obtained. The excavated clay usually comes in solid form, even when it contains 30 percent moisture. It is usually combined with soda ash to be reactivated and used. Bentonites usually contain some impurities such as quartz and gypsum and may require filtering and purifying before use as a building material.

One characteristic of bentonite clay, particularly the sodium type, is its ability to expand when water is added. This is due to the clay’s particles that are shaped like plates and make for a larger surface area. The water then exchanges ions with the particles and the clay can expand and swell in size.


The bentonite’s expanding ability makes it an ideal binding material, especially in metal castings, where the sand that contains the molten metal can be made from bentonite. The clay can also be mixed in cement for construction purposes. It can also perform as a sealant for holes created by drilling. Paints and dyes also include the clay as an ingredient, as bentonite is an excellent thickener.

The pet industry also has its uses for the clay, mainly for litter boxes. The moisture from the cats’ waste will be absorbed by the clay, which then turns into clumps and makes for easier disposal. Its cleansing ability also makes it an important ingredient for soaps and detergents, as the clay can bind with the dirt, and it can even make fabrics softer.

Bentonite has also been explored as a medication and is used for detoxification and indigestion purposes. In the same way that it binds to dirt, it can also attach itself to internal toxins and carry them as the clay is flushed out of the system. Its binding ability is also effective for oil spills, wastewater filtration, and even for purifying wines and vinegars.


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