Hydrated silica

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Hydrated silica is a form of silicon dioxide, which has a variable amount of water in the formula. When dissolved in water it is usually known as silicic acid. 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. Hydrated silica can be dehydrated to produce silica gel[citation needed], which is used as a desiccant. It is also used in various paints and varnishes and in the production of beer.


In its pure form, as manufactured for toothpaste, it is an odorless, tasteless, white, gelatinous substance, which is chemically inert.

Chemical formula[edit]

Chemical Formula: SiO2 · nH2O

1 SiO2 + 1 H2O → H2SiO3
1 SiO2 + 2 H2O → H4SiO4 [also known as Si(OH)4]
2 SiO2 + 1 H2O → H2Si2O5
2 SiO2 + 3 H2O → H6Si2O7
3 SiO2 + 2 H2O → H4Si3O8
3 SiO2 + 4 H2O → H8Si3O10
4 SiO2 + 1 H2O → H2Si4O9

Use in toothpaste[edit]

Diatomaceous earth, originally mined as "tooth powder" is a naturally occurring hydrated silica. As a fine gel abrasive, frequently combined with softer calcium carbonate (from chalk) it helps to remove plaque. Milled to a slightly larger size, the grains are more aggressive and are used in tooth bleaching formulations.

Flame retardant[edit]

It also has synergetic effects when compounded with traditional flame retardants such as magnesium hydroxide and aluminium hydroxide.[citation needed]


Hydrated silica is listed by the US Food and Drug Administration as "Generally Recognized as Safe".


Toothpaste: [1] Chemistry: [2][unreliable source?] Opal: [3] Paint/Varnish: [4] Beer: [5]