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Labradorite

labradorite
Rough labradorite (spectrolite) with play of color

Labradorite is the plagioclase feldspar most commonly faceted as a gem. It occurs in orange, yellow, colourless and red but the gemstone that shows a play of colour, or schiller, is the most popular to be used in jewellery. Labradorite having dark background with play of color is known as spectrolite.

Occurs in metamorphic and igneous rocks in Labrador (Canada), Finland, Norway and the former USSR.

Labradorite Pictures

Rough labradoriteLabradorite cabochons with play of color

Cause of Color : Play of color due to interference of light from twin planes.
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 :

Triclinic System


Cuts & Uses :

Facetted, cabochon, beads and carving.


Dispersion : 0.012
Hardness : 6.5
Lustre : Vitreous.
Magnification :

Oriented needles or platelets of magnetite, twin planes, fingerprints and crystal inclusions.


Optic Character :

Anisotropic, D.R.; Biaxial positive


Pleochroism : In dark colored labradorite.
Refractive Index / Birefringence :

1.560 – 1.572 / 0.009


Simulants (with separation tests) :
  • Transparent Labradorite from quartz (optic figure), scapolite (optic figure), beryl (optic figure), Iolite (pleochroism, inclusions, U.V. fluorescence)
  • Spectrolite from black opal (R.I., S.G., structure)

Sources :

U.S.A., India, Canada, Australia, Madagascar, Russia, Mexico.


Spectrum :

Not characteristic.


Synthesis :

None.


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