Magnesium carbonate (MgCO₃) is almost completely insoluble in water, but due to its crystal structure, is able to absorb large quantities of liquid water or moisture from the air. Since 1911, it has been added in small quantities to table salt to absorb moisture and allow the salt to flow freely when in humid conditions. Sold as “gym chalk”, it is used by rock climbers, weight lifters, and gymnasts to absorb moisture on hands and avoid the consequences of sweaty palms. It is non-flammable and completely nontoxic.