A clayey rock formed by the weathering of volcanic ash. It was named after the first place where it was found near Fort Benton in the US state of Wyoming. The mineral, also known as alumina, consists of calcium, sodium and aluminium silicates. It has a high adsorption capacity (accumulation of gases or dissolved substances) and a good swelling capacity and thus an increase in volume. In viticulture, low-swelling calcium bentonites or medium-swelling mixed bentonites (calcium and sodium) are used for various fining or stabilisation techniques such as protein or heat stabilisation. In this process, the thermolabile protein is removed. Untreated wines can already form heat turbidity at temperatures of 17 to 20 °C. The treatment can be carried out in the grape must or in the wine.