Difference between revisions of "Garnet"

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* PyrAlSpites (Pyrope, Almandine, Spessartite)
 
* PyrAlSpites (Pyrope, Almandine, Spessartite)
 
* UGrAndites (Uvarovite, Grossular, Andradite)
 
* UGrAndites (Uvarovite, Grossular, Andradite)
 +
 +
===Valency in isomorphous replacement===
 +
 +
The chemical formula of garnet is L<sub>3</sub>M<sub>2</sub>(SiO<sub>4</sub>)<sub>3</sub>, which means that the first element has a [[valency]] of 2<sup>+</sup>. Elements with the same valency can easily replace each other to form new chemical bonds, as in the case of garnet. One should not confuse the presence of trace elements with isomorphous replacement. Trace elements are not part of the "ideal" chemical makeup.
  
 
==Related topics==
 
==Related topics==
  
 
* [[Isomorphous replacement]]
 
* [[Isomorphous replacement]]

Revision as of 06:55, 8 December 2006

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

Basic

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:

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

Then there is a 6th series that hardly produces any minerals large enough to be cut to gemstones.

  • Uvarovite-Grossular

According to their 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)

Valency in isomorphous replacement

The chemical formula of garnet is L3M2(SiO4)3, which means that the first element has a valency of 2+. Elements with the same valency can easily replace each other to form new chemical bonds, as in the case of garnet. One should not confuse the presence of trace elements with isomorphous replacement. Trace elements are not part of the "ideal" chemical makeup.

Related topics