Bentonite clay is formed from ancient volcanic ash that was once exposed to seawater, at which point it absorbed a whole lot of minerals. It's often sourced from ancient seabeds (that are now dry land), and its name comes from Fort Benton, Montana—the location of the largest known deposit of bentonite clay. It's also called montmorillonite clay since this type of clay was first discovered in France's Montmorillon region.
Bentonite clay is part of the "smectite" group of clay that's known for an ability to expand when exposed to a liquid. It's rich in minerals, including silica, magnesium, calcium, sodium, copper, iron, and potassium.
There are two types of bentonite clay, depending on the ratio of key minerals they contain: sodium bentonite clay and calcium bentonite clay. They have similar properties, with subtle nuances.
Sodium bentonite draws more toxins out of the skin, and calcium bentonite is gentler and provides the skin with more minerals. While both types have their benefits, I prefer calcium bentonite for facial masks or using a mixture of the two for more congested skin."
Calcium bentonite clay, particularly green calcium bentonite clay, is also the type that's typically preferred for consumption (in small amounts, of course) when used for detoxification purposes, as it seems to be a bit gentler on the body.
While it may be relatively new to you, there's evidence that some of the earliest civilizations used clay to treat everything from aches and pains to infections and food poisoning. In ancient Mesopotamia (5000 to 3500 BCE), for instance, it's believed that people used a number of natural substances, including clays, to make poultices—mixtures of clay and water (or other wet ingredients like tea) wrapped in thin cloth and applied to the body to relieve pain and inflammation.