Difference between revisions of "Garnet"

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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:
 
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:
* Pyrope
+
* Pyrope (magnesium aluminum silicate)
* Almandine
+
* Almandine (iron aluminum silicate)
* Spessartite
+
* Spessartite (manganese aluminum silicate)
* Uvarovite
+
* Uvarovite (calcium chromium silicate)
* Grossular
+
* Grossular (calcium aluminium silicate)
* Andradite
+
* Andradite (calcium iron silicate)
  
 
According to similarities in the chemical composition, we can divide the above members of the garnet family into two groups.
 
According to similarities in the chemical composition, we can divide the above members of the garnet family into two groups.
  
* PyrAlSpites (Pyrope, Almandine, Spessartite)
+
* PyrAlSpites (Pyrope, Almandine, Spessartite) - the aluminium garnets
* UGrAndites (Uvarovite, Grossular, Andradite)
+
* 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.

Revision as of 06:26, 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 slighly 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)

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.

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