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.
Aluminum silicate of potassium, sodium and calcium. KAlSi
. Isomorphous series made up of Albite (Na), Oligoclase, Andesine, Labradorite, Bytownite and Anorthite (Ca) where the two end member are NaAlSi
Colors / Varieties:
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:
2.63 - 2.72
Cleavage / Fracture:
Easy 2 directional / Uneven.
; Biaxial positive
Refractive Index / Birefringence:
1.560 - 1.572 / 0.009
In dark colored labradorite.
Oriented needles or platelets of magnetite, twin planes, fingerprints and crystal inclusions.
Cause of Color:
Play of color due to interference of light from twin planes.
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)
Igneous rocks, pegmatite.
, India, Canada, Australia, Madagascar, Russia, Mexico.
Cuts & Uses:
Facetted, cabochon, beads and carving.