A clayey rock that was formed by the weathering of volcanic ashes. It was named after the first site near Fort Benton in the US state of Wyoming. Also known as clay, the mineral 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-swellable calcium bentonites or medium-swellable mixed bentonites (calcium and sodium) are used for various fining or stabilisation techniques such as protein or heat stabilisation. The thermolabile protein is removed. Untreated wines can form heat turbidity even at temperatures of 17 to 20 °C. The treatment can be carried out in grape must or in wine.