The basic unit of silicate, [SiO4]4- tetrahedron, can form single and
double chains and sheets.
LEARNING OBJECTIVE [ edit ]
Describe the various structures of silicates.
KEY POINTS [ edit ]
The basic building block of all silicate minerals is the [SiO4]4−tetrahedron.
Silicate minerals containing chains are termed inosilicates. In single chains (SiO32−)n, the silicon
to oxygen ratio is 1:3, while in double chains (Si4O116−)n, the silicon to oxygen ratio is 4:11 .
The formula of silicate sheet is (Si2O52−)n . Silicate minerals containing sheets are
termed phyllosilicates.
TERMS [ edit ]
Inosilicates
Inosilicates, or chain silicates, have interlocking chains of silicate tetrahedrons.
Silicate
A silicate (SiO44-) is a compound containing a silicon-bearing anion.
Phyllosilicates
Sheet silicate minerals, formed by parallel sheets of silicate tetrahedrons Si2O52-.
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SilicateTetrahedrons
The basic building block of all silicate minerals is the [SiO4]4−tetrahedron. There are four
covalent Si−O bonds. Each oxygenatom forms one vertex of the tetrahedron. The silicon to
oxygen atom ratio is 1:4.
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Silicate Tetrahedron
Ball­and­stick model of the silicate tetrahedron; red represents oxygen atoms and gray represents the
silicon atom in the center.
Silicate minerals containing isolated [SiO4]4− tetrahedrons are called nesosilicates or
orthosilicates.
Corner-Sharing Tetrahedrons
If two [SiO4]4− tetrahedrons share an oxygen atom at one common vertex, an [Si2O7]6− ion is
formed. The silicon to oxygen ratio is 2:7. Silicate minerals containing isolated
[Si2O7]6− double tetrahedrons are called sorosilicates.
Silicate Chains
Silicate minerals containing chains are termed inosilicates. They consist of single chains
(SiO32−)n, in which the silicon to oxygen atom ratio is 1:3, and double chains (Si4O116−)n, in
which the silicon to oxygen atom ratio is 4:11.
Double Chain
Ball­and­stick model of silicate double chains. Red balls correspond to oxygen, and gray to silicon atoms.
Asbestos
Asbestos (from Greek ἅ, unquenchable) is a group of fibrous silicate minerals containing
double chains. Prolonged exposure to dust containing fibres from certain types of asbestos is
now known to cause scarring of the lungs, lung cancer, and a particularly aggressive cancer
called mesothelioma. Mesothelioma is almost always fatal, with a median survival time of 11
months. Due to the exceptional danger posed by some absestos, certain counties now require
all work involving asbestos to be done by specialist companies. The vast majority of asbestos
is the so-called white form, which is not known to pose any real danger.
Silicate Sheets
SiO4 tetrahedrons can be arranged to form sheets. The formula of such a sheet can be written
(Si2O52−)n. Silicate minerals containing sheets are termed phyllosilicates.
Silicate Sheet
The formula of silicate sheet is (Si2O52−)n.
Three-dimensional Frameworks
Perhaps the most structurally complicated silicates are those based on networks of Si and O
that extend in all three dimensions. Examples of such minerals include quartz, zeolites, and
feldspars. Silicate minerals containing three-dimensional frameworks are termed
tectosilicates.
Three-dimensional structure of zeolite
In the mineral zeolite, silica and oxygen atoms are bonded layers of sheets.