If you’ve looked into clay for detox, skin health, or supplementation, you’ve probably seen montmorillonite and bentonite used almost interchangeably.
Some brands treat them as entirely different substances. Others collapse them into one vague “healing clay” category. Neither approach is particularly helpful, so let’s clear it up properly.
First things first: they’re closely related
Montmorillonite is a mineral. Bentonite is a clay. Bentonite clay is largely made of montmorillonite. In fact, montmorillonite is the dominant active mineral that gives bentonite its well-known properties: swelling, binding, and adsorption.
So when someone says “montmorillonite clay,” they’re usually describing a bentonite clay with a high montmorillonite content. This matters because not all bentonite clays are created equal.
What makes montmorillonite clay special?
Montmorillonite belongs to the smectite family of clays and has a layered structure with a natural negative electrical charge. This structure allows it to:
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Bind positively charged substances (including certain toxins and heavy metals)
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Absorb water and swell
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Create a large surface area relative to its size
These properties are what make montmorillonite-rich clays popular for detox protocols, skincare masks, and even some veterinary uses. The higher the montmorillonite content, the more pronounced these effects tend to be.
So what exactly is bentonite clay?
Bentonite is a naturally occurring clay formed from volcanic ash. Its composition varies depending on where it’s mined.
Most bentonite contains:
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Montmorillonite (the key functional mineral)
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Smaller amounts of other minerals such as feldspar, quartz, and calcite
This is why two bentonite clays can behave very differently: one might swell dramatically and bind strongly, while another barely does either. When a label simply says “bentonite clay” without further detail, it tells you very little.
Does the difference between montmorillonite and bentonite matter in real life?
Yes, depending on how you intend to use it.
For internal use (edible clay)
Montmorillonite content matters because it directly affects binding capacity. Equally important are:
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Purity
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Heavy metal testing
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Particle size
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How the clay is processed and handled
“Natural” alone isn’t enough here.
For skin applications
A montmorillonite-rich bentonite will generally:
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Draw more oil and impurities
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Be more active on congested or inflamed skin
That can be helpful, or too aggressive, depending on skin type and frequency of use.
Montmorillonite vs bentonite isn’t really an either/or question. The better question is:
What is the mineral composition, quality, and testing behind the clay you’re using?
When brands rely on vague language instead of specifics, it’s usually because they don’t have much to show. Clear sourcing, clear testing, and clear explanations matter far more than whichever word appears on the front of the jar.
