Healing Clays of the World ~ Illite, Bentonite, Montmorillonite - Eytons' Earth


Bentonite: Public Research Project

Bentonite & Montmorillonite: Smectite Clay Minerals


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Featured: Did You Know...?

  Researchers at the University of New England in Australia claim to have made a surprising discovery. While searching for means to combat a serious stomach disorder common to Australian sheep, they found that "small quantities of a naturally occurring clay, called bentonite, mixed into a sheep's drinking water" not only improved the animal's digestion but increased wool growth, reports The Australian. One of the researchers, Professor Ron Leng, said that a daily dose of a half ounce of bentonite mixed into their drinking water had resulted in increase of up to about one tenth of an ounce a day in a sheep's growth. It is hoped that use of this mixture on sheep nationwide will bring increases in wool production worth millions of dollars.

-AWAKE! 6/22/88

Quick Links to Articles in this Section

|| What is Bentonite? || Bentonite Clay Mineral Formation & Evolution ||
|| Hydrated Sodium Bentonite Studies - Edible Clay || Bentonite & Food Poisoning ||
|| Pascalite Article - White Calcium Bentonite || Clay Use by Primitives & Indigenous Cultures ||
|| Trace Minerals and Clay || Living Clay: Bentonite ||

What is Bentonite? And Montmorillonite?

Bentonite Hills - Click for larger view
Bentonite Hills - Click for larger view

Bentonite Hills in Capitol Reef National Park
Photo used with Permission, copyright Q.-T. Luong

Bentonite Hills - Capitol Reef National Park
Photo used with Permission, copyright Q.-T. Luong

Bentonite Micrograph

Bentonite Micrograph

Green Bentonite - Nebraska


Bentonite is a name given to a particular clay that was originally found in Fort Benton, Eastern Wyoming. The name was given by W.C. Knight in 1898. Previously, it was called Taylorite, which was named after William Taylor, who first began to draw attention to the clay deposits.

Geologists often describe bentonite as a clay mineral containing Montmorillonite, which poses a rather curious problem, as Montmorillonite is a name of a particular clay that was discovered in Montmorillon, France, named by Mauduyt in 1847.

"The name montmorillonite is used currently both as a group name for all clay minerals with an expanding lattice, except vermiculite, and also as specific mineral name. Specifically it indicates a high-aluminia end member of the montmorillonite group with some slight replacement of Al3+ by Mg++ and substantially no replacement of Si4+ by Al3+. MacEwan suggested the term montmorillonoid for the group name to avoid confusion with montmorillonite as a specific mineral name, and Correns suggested Montmorin as the group name. Neither of these names has found favor. The name smectite suggested as a group name by the Clay Minerals Group of the Mineralogical Society of Great Britain at the outset met strong opposition, particulary by many American mineralogists, but it is becoming widely accepted."

(R. E. Grim: Clay Mineralogy 2nd edition, McGraw-Hill Book Company, New York (1968) 41).

Bentonite Chemical Equation: Al2O34SiO2H2O ( Reade Advanced Materials )
Montmorillonite Chemical Equation: Na0.2Ca0.1Al2Si4O10(OH)2(H2O)10

"Sodium bentonite is the name for the ore whose major constituent is the clay mineral, sodium montmorillonite. Montmorillonites are three-layer minerals consisting of two tetrahedral layers sandwiched around a central octahedral layer (Figure 1). Oxide anions at the apices of the tetrahedral subunits are directed inward where they surround interior aluminum, iron and magnesium cations, thereby forming the octahedral subunits of the octahedral layer. Bonding, between the shared interior oxide anions and the cations in both the tetrahedral and the octahedral layers, links the layers together and yields the unique sheet structure characteristic of clay minerals. For montmorillonite, the total negative charge contributed to the structure by the sum of all the oxide anions (O2-) is somewhat in excess of the total positive charge contributed by the sum of all the structural cations (Si+4, Al+3, Fe+2, Fe+3, Mg+2) and imparts a slight overall negative charge to the surfaces of the clay sheets. This slight excess negative charge on the sheets is counterbalanced by free-moving (exchangeable) cations which exist between them. These three layers in each sheet comprise individual bentonite platelets which are typically 1 nm in thickness and 0,2-2 microns in diameter. Dry platelets of sodium bentonite are most commonly grouped together in a face-to-face arrangement, with exchangeable cations and small amounts of adsorbed wares in an interlayer region between each platelet. The thickness of the interlayer region is variable depending on the amount of water adsorbed between the platelets."

If the terms bentonite and montmorillonite had both been coined late in the 20th Century, then it's possible that one would be saying that " Sodium montmorillonite is the name for the ore whose major constituent is the clay mineral, sodium bentonite."

To fully illustrate this, consider the following classification made by American Colloid, one of the premiere Bentonite mining organizations in the United States:

Bentonite - HPM20:

"High-purity, air-classified sodium bentonite, selectively-mined, consisting of micronized particles and supplied as a free-flowing powder. This high-purity montmorillonite is typically used where small particle size is required in pesticide and fertilizer applications... A Hydrous aluminum silicate, air purified to concentrate the finest montmorillonite fraction from the bentonite ore. Contains traces of feldspar, quartz, calcite, and gypsum."


We wanted to add the above paragraphs due to the common misconception that, somehow, bentonites and montmorillonites are two different types of mineral classes. In other words, we've talked to people who didn't want bentonite, but instead montmorillonite, and those who have rejected montmorillonite because it wasn't labelled as bentonite.

Bentonites (and montmorillonites) are further classified by their dominant cation (the element in the clay that has the highest potential for ion exchange).

Some sources state that there are only two primary types (sodium and calcium) of bentonite. However, magnesium bentonite (http://www.gsaresources.com/bentonite.htm), calcium magnesium bentonite, and potassium bentonite (http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_indiana.html), while less common, are unique forms of bentonite, just like the calcium and sodium bentonites.


Featured: Did You Know...?

  "What is the evolutionary significance of plant toxins and animal anti-toxin behaviour? From a plant's evolutionary perspective, a seed should be high in nutrients to support germination and seedling growth; the ripe fruit around the seed should also be nutrient-rich and attractive to animals, encouraging them to pluck and eat the fruit and disperse the seed. On the other hand, the seed itself should be repulsive to animal consumers, inducing them to regurgitate or defaecate it, and the unripe fruit should be repulsive, lest animals harvest it before the seed is viable. From an animal's evolutionary perspective, an ability to defeat the plant's toxin defences would enable it to obtain the nutrients in the seed as well as those in the ripe fruit, and to outcompete other animal consumers by harvesting the fruit while it is unripe and still unpalatable to them.

"Any textbook of animal biology describes the resulting evolutionary arms race, in which plants evolve increasingly potent toxins (such as strychnine and quinine), and animals evolve increasingly potent means of detoxification. While enzymatic detoxification has previously received the most attention, the work of Gilardi et al.10 and the wide distribution of geophagy among animal herbivores suggest an additional important means of detoxification by adsorption on ingested soil minerals."

- Jared M. Diamond, Department of Physiology, University of California Medical School, Los Angeles

Read more about indigenous habits and instinctual use of edible clay minerals in our bentonite articles section.


Green healing clay, bentonite, Fuller's Earth, Montmorillonite

See Also:


General Uses of Healing Clay
Introduction to Healing Clays of the World


Eytons' Earth - Clay Chemistry




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Topic: bentonite-montmorillonite.php
4/5 (3)
Jun 2017
Daniele (Singapore) says...
Don't you think that (O=) after oxide anions should be written as (O2-)
[2- is in superscript]

Hi Daniele:

Actually, now that you mention it, yes I do!

That quote was a copy/paste from Cetco, and was either a typo by them or a mistake by me. 

I will change it, thanks for noticing and letting me know!

Jan 2017
Mellen (Yarmouth) says...
Hi- just confused,

this sentence states:

Bentonites (and montmorillonites) are further classified by their dominant anion (the element in the clay that has the highest potential for ion exchange).

Wouldn't they be classified by the dominant CATION? i.e. sodium (Na+), calcium (Ca+2), etc??

Greetings, Mellen:

Thank you for catching that typo.  You are absolutely correct!  I have made the correction.

Thank you for taking the time to point it out.


Swapnil Thakur
Mar 2016
First Poster
Swapnil Thakur (Thane) says...
Can you add sources for Sodium bentonite/?
that will be much helpful for those looking to source sodium bentonite.

Thank You

Greetings, Swapnil:

We have a page on recommended sources if you use the top nav menu.  At this time, my favorite sodium bentoonite is a high yield sodium bentonite that complies with USP standards.  It is ultra ventilated and water washed.  You can find it @greenclays.com

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~ New Articles Section on bentonite and clay minerals - the clay cure ~
|| what is bentonite? || bentonite clay mineral formation & evolution ||
|| hydrated sodium bentonite studies - edible clay || bentonite & food poisoning ||
|| Pascalite article - white calcium bentonite || clay use by primitive & indigenous cultures ||
|| trace minerals and clay || living clay: bentonite || healing clay therapy books ||
Silver, Clay and Ozone Heal a Broken Infected Finger || Stinging Trees of Australia & Healing Clay
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Eytons' Earth, a non-commercial, public awareness organization dedicated to researching the values of healing clays ( bentonite, illite, and montmorillonite ), is based out of Las Vegas Nevada. Feel free to us at any time. While we are not always able to respond, we do our best to answer non-commercial inquiries!

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