Difference between revisions of "Garnet"

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{{garnet}}
 
{{garnet}}
  
Garnet is the family name given to a series of members, with a common crystal habit and slighly different chemical make-up ([[Isomorphous_replacement|isomorphous]]). The following are the 6 members of the garnet family:
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Garnet is the family name given to a series of members, with a common crystal habit and slightly different chemical make-up ([[Isomorphous_replacement|isomorphous]]). The following are the 6 members of the garnet family:
 
* Pyrope (magnesium aluminum silicate)
 
* Pyrope (magnesium aluminum silicate)
 
* Almandine (iron aluminum silicate)
 
* Almandine (iron aluminum silicate)
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* Grossular (calcium aluminium silicate)
 
* Grossular (calcium aluminium silicate)
 
* Andradite (calcium iron silicate)
 
* Andradite (calcium iron silicate)
 
According to similarities in the chemical composition, we can divide the above members of the garnet family into two groups.
 
 
* PyrAlSpites (Pyrope, Almandine, Spessartite) - the aluminium garnets
 
* UGrAndites (Uvarovite, Grossular, Andradite) - the calcium garnets
 
  
 
All the above members are rarely found with an ideal chemical make-up, instead they form isomorphous series. Most gem quality garnets belong to either of the following 5 isomorphous series and their chemical composition is an intermediate between the two endmembers mentioned.
 
All the above members are rarely found with an ideal chemical make-up, instead they form isomorphous series. Most gem quality garnets belong to either of the following 5 isomorphous series and their chemical composition is an intermediate between the two endmembers mentioned.
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* Pyrope-Grossular
 
* Pyrope-Grossular
 
* Grossular-Andradite
 
* Grossular-Andradite
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 +
According to the tendency to form isomorphous series between members, we can divide the above members of the garnet family into two groups (although these two groups can mix).
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 +
* PyrAlSpites (Pyrope, Almandine, Spessartite)
 +
* UGrAndites (Uvarovite, Grossular, Andradite)

Revision as of 07:39, 8 December 2006

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Garnet
Chemical composition L3M2(SiO4)3

Isomorphous series

Crystal system Cubic
Habit Dodecahedra
Cleavage None
Hardness 6.5-7.5
Optic nature Isotropic
Refractive index 1.74-1.89
Birefringence None
Specific gravity 3.60-4.20
Lustre Vitreous to sub-adamantine

Garnet is the family name given to a series of members, with a common crystal habit and slightly different chemical make-up (isomorphous). The following are the 6 members of the garnet family:

  • Pyrope (magnesium aluminum silicate)
  • Almandine (iron aluminum silicate)
  • Spessartite (manganese aluminum silicate)
  • Uvarovite (calcium chromium silicate)
  • Grossular (calcium aluminium silicate)
  • Andradite (calcium iron silicate)

All the above members are rarely found with an ideal chemical make-up, instead they form isomorphous series. Most gem quality garnets belong to either of the following 5 isomorphous series and their chemical composition is an intermediate between the two endmembers mentioned.

  • Pyrope-Almandine
  • Pyrope-Spessartite
  • Spessartite-Almandine
  • Pyrope-Grossular
  • Grossular-Andradite

According to the tendency to form isomorphous series between members, we can divide the above members of the garnet family into two groups (although these two groups can mix).

  • PyrAlSpites (Pyrope, Almandine, Spessartite)
  • UGrAndites (Uvarovite, Grossular, Andradite)