The Silicate
Group
The silicate mineral group is of the
most important because they continue about 90% of the earth's crust, occurring
as the major constituents of most igneous rocks and in appreciable quantities
in sedimentary( except limestone) and metamorphic varieties as well. most common silicate mineral are made up
chiefly of a few of the following 9 element Na, K, Al, Mg, Fe, Li, Si and O.
These include minerals such as quartz, feldspar, mica, amphibole, pyroxene,
olivine, and a great variety of clay minerals.
Every Silicate mineral contains Oxygen and Silicon.
The basic unit in all silicate mineral is the Silicon-oxygen tetrahedron. The
silica tetrahedron, a combination of four oxygen atoms and one silicon atom.
These are arranged such that planes drawn through the oxygen atoms form a
tetrahedron. Since the silicon ion has a charge of +4 and each of the four
oxygen ions has a charge of –2, the silica tetrahedron has a net charge of –4.
Type
|
Similar names
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Ratio
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Examples
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Nesosilicates
|
orthosilicates, independent tetrahedra
or island silicates
|
Si:O = 2:7
|
olivevin
Zircon
gypsum
kyanite
|
Cyclosilicates
|
Ring silicates
|
Si:O = 1:3
|
Beryl and tourmaline ( all hexagonal
system)
|
Inosilicates
|
Chain silicates
|
Single chain
Si:O = 1:3
Double chain
Si:O = 4:11
|
single chain
pyroxenes, Asbestos
Double chain
Enstalite, Amphiboles
|
Phyllosilicates
|
Sheet silicates
|
Si:O = 2:5
|
Mica, chromite and
kaolinite (Al is an imp.)
|
Tectosilicates
|
Framework silicates and network
structure
|
Si:O = 1:2
|
Quartz feldspar and felspathoid
|