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Feldspar

feldspar
Microcline feldspar from Mongolia

Feldspar is a group of minerals which comprises a number of species with varying degrees of isomorphism. Feldspars are subdivided into two sub group, potassium feldspars (orthoclase, microcline) and plagioclase feldspar.

Of gem interest are orthoclase, microcline and plagioclase (albite, labradorite and oligoclase).

Cause of Color : In all species chatoyancy and asterism is due to the presence of parallel, oriented inclusions.
Chemical Composition :

Aluminum silicate of potassium, sodium and calcium. KAlSi3O8. Isomorphous series made up of Albite (Na), Oligoclase, Andesine, Labradorite, Bytownite and Anorthite (Ca) where the two end member are NaAlSi3O8 and CaAl2Si2O8.


Crystal System / Forms :

Well formed crystals as well as massive or tabular habits. Commonly exhibit lamellar twinning.


Dispersion : 0.012
Lustre : Vitreous
Optic Character :

Anisotropic, D.R.


Spectrum :

Not characteristic


Synthesis :

None


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