The facts
What bentonite actually is
Bentonite is classified as a clay rock formed by the in-situ alteration of volcanic ash, dominated by the swelling smectite mineral montmorillonite, with the composition Montmorillonite (Na,Ca)0.33(Al,Mg)2Si4O10(OH)2.nH2O. It crystallises in the aggregate (monoclinic smectite) system.
Colour comes from cream, grey, green and olive; iron content drives the colour and is graded for cosmetic use, which is also what a laboratory looks at when it is asked whether a colour is natural.
Refractive index 1.48-1.60. Specific gravity around 2.00-2.70 (varies with hydration state). Cleavage: perfect basal in the clay platelets. Those three numbers separate it from most of what imitates it.
Where bentonite comes from
Bentonite is produced at Black Hills, Wyoming, Montana and South Dakota, USA - the sodium bentonite standard, Milos, Cyclades, Greece - the largest European producer, Kutch, Gujarat, India, Cankiri and Ordu, Turkiye and Bavaria, Germany; Fuling, Chongqing, China.
The locality is part of the description, not a footnote — two stones of the same weight from two of these places are not the same stone.
How bentonite is treated
Dried, milled, and frequently soda-activated - calcium bentonite treated with sodium carbonate to make it swell like the sodium form, a very common and often undisclosed conversion. Uses: drilling mud (the original and still major one), foundry sand binder, iron-ore pelletising, cat litter, geosynthetic clay liners for landfills, civil-engineering slurry walls, wine fining, and cosmetics. The cosmetic and 'detox' clay market makes health claims that are not supported; some bentonites also carry elevated lead and arsenic, and the US FDA has issued warnings on specific clay products.
Treatment changes value, sometimes by a multiple, so it belongs in the description before the price and not after the sale.
What bentonite is confused with
In the trade bentonite is most often mistaken for, or substituted by, Kaolin and fuller's earth (non-swelling clays), Attapulgite / palygorskite, Soda-activated calcium bentonite sold as natural sodium bentonite or Synthetic hectorite.
The separation is rarely a matter of opinion: refractive index 1.48-1.60 and specific gravity 2.00-2.70 (varies with hydration state) settle most of it in a minute, and magnification settles the rest.
What bentonite is used for
Demand for bentonite comes from drilling fluids, heavy industry, cosmetics, filtration and kitchen and table, which is why one price per carat never covers it.
We quote each application in the unit that trade actually buys in, by the tonne or by the piece.
Durability and care
Bentonite is 1-2 on the Mohs scale, with perfect basal in the clay platelets cleavage.
Below about 5.5 a stone will be scratched by ordinary household dust, which is largely quartz. That does not make it unusable — it makes it a pendant, an earring or an object rather than a ring worn every day.
Warm water, mild soap and a soft brush. Avoid ultrasonic cleaners on anything fracture-filled, stabilised, dyed or visibly included.
What bentonite costs
As a guide, bentonite trades around $60-150 per tonne for common grades; API drilling grade and specialty cosmetic grades $200-600 per tonne.
That is a range, not a quote. Colour, size, clarity, cut and origin move the figure a long way inside it, and the only honest price is one given against a specific stone. Send us what you need and we will price it.
Questions
Is bentonite treated, and how?
Dried, milled, and frequently soda-activated - calcium bentonite treated with sodium carbonate to make it swell like the sodium form, a very common and often undisclosed conversion. Uses: drilling mud (the original and still major one), foundry sand binder, iron-ore pelletising, cat litter, geosynthetic clay liners for landfills, civil-engineering slurry walls, wine fining, and cosmetics. The cosmetic and 'detox' clay market makes health claims that are not supported; some bentonites also carry elevated lead and arsenic, and the US FDA has issued warnings on specific clay products.
Where does bentonite come from?
Black Hills, Wyoming, Montana and South Dakota, USA - the sodium bentonite standard, Milos, Cyclades, Greece - the largest European producer, Kutch, Gujarat, India, Cankiri and Ordu, Turkiye and Bavaria, Germany; Fuling, Chongqing, China. Origin affects price, so we name the locality rather than the country on every quote.
Is bentonite hard enough to wear every day?
Not really. At 1-2 on the Mohs scale it is softer than the quartz dust in ordinary household dirt, so it scratches with wear. It suits pendants, earrings and objects better than a daily ring.
How much does bentonite cost?
Indicatively $60-150 per tonne for common grades; API drilling grade and specialty cosmetic grades $200-600 per tonne. Colour, size, clarity and origin move the price a long way within that, so treat it as a range and ask for a quote against a specific stone.
What is bentonite confused with?
Most often Kaolin and fuller's earth (non-swelling clays), Attapulgite / palygorskite, Soda-activated calcium bentonite sold as natural sodium bentonite and Synthetic hectorite. A refractive index of 1.48-1.60 and a specific gravity near 2.00-2.70 (varies with hydration state) separate it quickly.
What is bentonite used for besides jewellery?
drilling fluids, heavy industry, cosmetics, filtration and kitchen and table. Each of those trades buys it in a different form and a different unit.
Related stones
Looking for bentonite?
Tell us the size, the quality and what it is for. We source it, photograph it and quote it — with the locality named.
Ask about bentonite