Bentonite Clay
Bentonite clay is the mineral equivalent of a thirsty sponge. Formed from volcanic ash aged in prehistoric inland seas, it consists chiefly of montmorillonite – a layered aluminosilicate featuring platelet sheets with negative charges that attract cations like sodium, calcium, and magnesium. When mixed with water, the platelets swell up to fifteen times their dry volume, creating a gel matrix that can entrap oils, heavy metals, and bacterial toxins through adsorption and cation exchange.
In skin care, this swelling translates to pore-purging masks that visibly mattify and tighten within ten minutes. Instrumental Sebumeter readings show a 25-to-40-percent reduction in surface lipids following a single bentonite mask, and a 2019 Journal of Cosmetic Science paper documented modest but clear declines in Propionibacterium acnes colony counts on treated foreheads. The electrostatic attraction seizes positively charged impurities, while mild astringency triggers vascular constriction, momentarily shrinking the appearance of pores.
Yet the clay’s wicking strength can backfire. Left to dry until cracking, bentonite continues to pull water – not just sebum – from the epidermis, leaving dehydrated patches. The solution is the “moist mask” method: spritz the face with a hydrating mist the moment edges turn pale, keeping the clay flex-point damp until rinse-off. Modern formulations incorporate humectants such as glycerin or beta-glucan to counterbalance.
Bentonite’s detox reputation extends to heavy-metal chelation. In vitro tests show it binds lead, cadmium, and mercury ions, but topical relevance remains speculative because the stratum corneum rarely stores such metals in meaningful amounts. However, bentonite can calm poison-ivy rashes by adsorbing urushiol resin – anecdotally supported and now the subject of small clinical trials.
Quality matters. Pharmaceutical-grade bentonite undergoes gamma irradiation to kill spores like Bacillus cereus that survive arid conditions. Food-grade clays sourced from the Fort Benton formation in Wyoming boast consistent cation-exchange capacity, whereas unvetted overseas supplies may contain silica dust or arsenic contaminants. Responsible brands publish elemental analyses and microbial specs.
Practical usage: mix one tablespoon of clay with equal parts water or raw honey, apply a 1-mm layer, keep moist for up to ten minutes, and rinse in lukewarm water. Follow with a ceramide-rich serum. Use no more than twice weekly for oily skin; once weekly suffices for combination types. Those on isotretinoin or using exfoliating acids daily should tread lightly – bentonite will amplify dryness if the barrier is already fragile.
Bentonite (/ˈbɛntənaɪt/ BEN-tə-nyte) is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-montmorillonite.
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Bentonite usually forms from the weathering of volcanic ash in seawater, or by hydrothermal circulation through the porosity of volcanic ash beds, which converts (devitrification) the volcanic glass (obsidian, rhyolite, dacite) present in the ash into clay minerals. In the mineral alteration process, a large fraction (up to 40–50 wt.%) of amorphous silica is dissolved and leached away, leaving the bentonite deposit in place.[citation needed] Bentonite beds are white or pale blue or green (traces of reduced Fe2+
) in fresh exposures, turning to a cream color and then yellow, red, or brown (traces of oxidized Fe3+
) as the exposure is weathered further.
As a swelling clay, bentonite has the ability to absorb large quantities of water, which increases its volume by up to a factor of eight. This makes bentonite beds unsuitable for building and road construction. However, the swelling property is used to advantage in drilling mud and groundwater sealants. The montmorillonite / smectite making up bentonite is an aluminium phyllosilicate mineral, which takes the form of microscopic platy grains. These give the clay a very large total surface area, making bentonite a valuable adsorbent. The plates also adhere to each other when wet. This gives the clay a cohesiveness that makes it useful as a binder and as an additive to improve the plasticity of kaolinite clay used for pottery.
One of the first findings of bentonite was in the Cretaceous Benton Shale near Rock River, Wyoming. The Fort Benton Group, along with others in stratigraphic succession, was named after Fort Benton, Montana, in the mid-19th century by Fielding Bradford Meek and F. V. Hayden of the U.S. Geological Survey. Bentonite has since been found in many other locations, including China and Greece (bentonite deposit of the Milos volcanic island in the Aegean Sea). The total worldwide production of bentonite in 2018 was 20,400,000 metric tons.
