In nature, silicon occurs exclusively in
oxidized form, as the compounds silicon
dioxide and silicates. Silicon is the second
commonest element in the Earth’s solid
crust, accounting for 25.8 percent by
weight, and the most important component
of inorganic materials. Since silicon is
very rarely found as an element in nature,
it was not isolated until relatively recently.
On the other hand, siliceous construction
and engineering materials, such as sand,
clay and ceramics, have been available
since time immemorial.