Hyrated Silica is a form of silicon dioxide, which has a variable amount of water in the formula. It is also known as silicic acid, a term usually used for its form dissolved in water. It is found in nature, as opal, which has been mined as a gemstone for centuries and in the cell walls of diatoms. It is also manufactured for use in toothpaste. Once dehydrated the gel is used as a dessicant known as Silica Gel. It is also used in various paints and varnishes and in the production of beer.