Hydrated silica

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Hydrated 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 desiccant known as silica gel. 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 odourless, tasteless, white, gelatinous substance, which is chemically inert.

Chemical formula[edit]

Chemical Formula: SiO2 · nH2O

SiO2 = 1,   H2O = 1:    H2SiO3 
SiO2 = 1,   H2O = 2:    H4SiO4 [also known as Si(OH)4]
SiO2 = 2,   H2O = 1:    H2Si2O5 
SiO2 = 2,   H2O = 3:    H6Si2O7 
SiO2 = 3,   H2O = 2:    H4Si3O8 
SiO2 = 3,   H2O = 4:    H8Si3O10 
SiO2 = 4,   H2O = 1:    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] Opal: [3] Paint/Varnish: [4] Beer: [5]