Hydrated silica is the abrasive used in gel toothpastes, or in the
clear portion of striped toothpastes. It is often used in opaque
toothpastes as well, as a secondary abrasive.
When dried in an oven, hydrated silica looses the water, and
becomes a dessicant, a substance that attracts water
from the air. You find little packets of "silica gel" crystals
in containers whose contents will be damaged by condensing
moisture, such as vitamin bottles, consumer electronics, pepperoni,
or leather products.
Silica gel can be made by reacting an acid with sodium silicate
(sold in drug
stores as "water glass" or "egg keep", and used to paint eggs to
seal them from air, preventing spoilage). Drying
the resulting gel will get the dessicant, or it can be used wet
You can find sodium silicate in the colorful "Magic Rocks" seen
in gift shops at museums. The dry form is mixed with salts of
various metals. When you drop them in water, the sodium is replaced
by the metal. The resulting metallic silicate is not soluble in
water, and has a color characteristic of the metal (e.g. copper
is blue). The metallic silicate is also a gel, so it expands,
and grows into colorful stalagmites in the water.
hydrated silica: InChI=1/H2O3Si/c1-4(2)3/h1-2H