Perlite is a siliceous volcanic glass with many uses in construction, horticulture, and the beverage industry. It is mined in North America, South America, Asia, Australia, and Europe and used in its puffed form as a filter aid. Perlite aids filtration by increasing the length of time before a filter becomes clogged with solids. It can also be used as a precoat on which other grades of filtering agents can be applied. For example, a pressure leaf filter can be precoated with perlite, upon which subsequent layers of diatomaceous earth can be applied to form a layered cake. Perlite used in conjunction with other filter media helps brighten beer by trapping suspended solids, like yeast and hop particles, that otherwise might end up in a bright beer tank and subsequently in the packaged product. Use of perlite is popular because it can reduce the amount of diatomaceous earth needed for filtration. Diatomaceous earth, when dispersed into the air, is associated with respiratory problems.