Labradorite

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

Labradorite Properties

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.
Colors / Varieties: 
Plagioclase:
  • Albite: Moonstone (orthoclase-albite)
  • Labradorite: Transparent (white, grey, yellow); Phenomena: chatoyancy, asterism, play of color i.e., labradorescence); Spectrolite: dark background with play of color.
  • Oligoclase: Sunstone: Phenomena: aventurescent, chatoyancy
Crystal System / Forms: 
Triclinic System
Hardness: 
6.5
Specific Gravity: 
2.63 - 2.72
Cleavage / Fracture: 
Easy 2 directional / Uneven.
Optic Character: 
Anisotropic, D.R.; Biaxial positive
Lustre: 
Vitreous.
Refractive Index / Birefringence: 
1.560 - 1.572 / 0.009
Pleochroism: 
In dark colored labradorite.
Dispersion: 
0.012
Magnification: 
Oriented needles or platelets of magnetite, twin planes, fingerprints and crystal inclusions.
U.V. Fluorescence: 
Variable.
Spectrum: 
Not characteristic.
Cause of Color: 
Play of color due to interference of light from twin planes.
Treatment (Enhancement): 
None.
Synthesis: 
None.
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)
Geological Occurrence: 
Igneous rocks, pegmatite.
Sources: 
U.S.A., India, Canada, Australia, Madagascar, Russia, Mexico.
Cuts & Uses: 
Facetted, cabochon, beads and carving.