DEPARTMENT OF GEOLOGY
The silicate mineral group is of great importance because they
constitute about 90% of the earth’s crust. they are found in all
the common rocks except limestone(caco3)
Every silicate minerals contains oxygen and silicon .
The Basic unit in all silicate minerals is the silica –oxygen
Here the structures is composed of oxygen atoms and silicon
atom at centre .
These tetrahedra can occur in the silicate structure
either as single units or join into chains, sheet and
three dimensional network by sharing oxygen atoms
The silicate structure classified into 6 major types by
Depending upon their atomic structure .
Neosilicates Sorosilicates Cyclosilicates Inosilicates Phyllosilicates Tectosilicates
Single chain silicates Double chain silicates
It is a independent tetrahedra (sio4).
The atomic packing of Neososilicates structure is
generally dense which causes the mineral of this group to
have relatively high specific gravity and hardness.
The crystal habit of these minerals generally
equidimensional and they have poor cleavage .
Ex:-Olivine [(MgFe )sio4].
The sorosilicates are characterized by linked pairs
of Sio4 tetrahedra.
In this two tetrahedra sharing one oxygen.
The ratio of si : o= 2:7,
Ex :-Hemimorphite [Zn4(si2o7)],
The cyclosilicates contain rings of linked Sio4
tetrahedra having a ratio of Si:O=1:3 .
These rings may consist of groups of three, four ,or six
liked tetrahedra .
cyclosilicate minerals are extremely strong minerals.
Ex:- Beryl [Be3Al2Si6o18 ]
Inosilicates are divided into two group based on there
arrangement of tetrahedra ,such as
I. Single chain silicates :-In this group tetrahedra are linked by
sharing oxygen's to form straight chain of indefinite length ,
The ratio of Si:O= 1:3.
I. Double chain silicates :- In this group formed by adjacent of two
single chains with sharing of oxygen atoms between two tetrahedra ,
The ratio of Si:O= 4:11.
This mineral commonly form needle like crystals(Asbestos)
Ex:-Amphibole group minerals .
The Phyllosilicates form sheet structure in which
there is the continuous linking of hexagonal group of
silica tetrahedra .
In this structure three of four oxgens in each sio4
tetrahedron are shared with neighbouring tetrahedra
giving ratio of Si:O=2:5 .
Ex:- Micas, chlorites, and kaolinite.
In Tectosilicates sio4 tetrahedra are linked in three
dimensional frame work .
All oxgens in each sio4 tetrahedron shared with
neighbouring tetrahedra and giving ratio of si:o=1:2.
Which mineral belong to tetosilicates group posses
uniform properties .
Ex:- Quartz ,Feldspars group of minerals .