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The Silicate stuctures


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The Silicate stuctures

  2. 2. 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 tetrahedron. sio4 ------  Here the structures is composed of oxygen atoms and silicon atom at centre .
  3. 3. 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 . Silicate structures Neosilicates Sorosilicates Cyclosilicates Inosilicates Phyllosilicates Tectosilicates Single chain silicates Double chain silicates
  4. 4. 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]. Zircon (ZrSio4). Garnet.(CaAl2Sio3O12)
  5. 5.  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)], Melilite (CaMgSi2o7) si si
  6. 6.  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 ] Tourmaline .
  7. 7. 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. Ex:-pyroxenes, 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 .
  8. 8. 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.
  9. 9.  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 .