Labradorite: Gemstone Information 

A common constituent of anorthosites, norites, basalts and gabbros as well as other igneous rocks. In the metamorphic environment it occurs in gneisses derived from basic rocks. It is found in Canada (Tabor Island,
Nain area of Labrador, Newfoundland Province – extensive rock-like masses), Madagascar (striped labradorite from Bekily, the bands, due to twinning showed exsolution labradorescence). Blue ‘flashing’ labradorite
from India is reported to show a similar effect as the light source, relative to the stone, is moved. Blue labradorescent twinning bands become dark and vice versa. Found in Tanzania; Mexico, Russia, Brazil and widely
distributed throughout the USA (in addition to the commercial Oregon deposits of faceting-grade labradorite (see sunstone).
Gem-quality material has been recovered from localities in Arizona, California – Mode County (sunstone), New Mexico, Nevada and Utah – Sunstone Knoll, Millard County – yellow transparent; RI 1.565–1.572; SG 2.68 {similar material comes from Mexico and Australia, Hogarth Range, New South Wales, and near Springsure, Queensland – pale yellow transparent RI 1.556–1.564; SG 2.695}). Anorthosite rocks host iridescent labradorite at the very large Golovinskoe deposit in the Volyn district which part of the western Ukraine shield and at Dzhugdzhurskoe in the east of the Aldan shield, Russia.
The normal rock-like labradorite is also found at other localities in Newfoundland, along the shore of Lake Huron, at Cape Mahul, at Abercrombie and at Morin in Quebec Canada. In Russia it occurs in the Ukraine especially at Gorodishch in the Zhitomir district, and in the Ural Mountains. In the USA small quantities occur in Arkansas, New Mexico and Vermont.

Appearance
Transparent to translucent. Simple and polysynthetic twinning are ubiquitous. The latter may cause a grooved effect on crystal and cleavage surfaces that appear as striations. Usually massive.
• Lustre: Vitreous
• Colour: Usually colourless, white, greyish, pale yellow, bluish grey or greenish, with greyish massive material often showing a distinctive play of colours (‘labradorescence’) normally blue and green but can be yellow, golden, red and purple.
Varieties
Sunstone
‘Sunspar’
(RI 1.560–1.568) with a chemical composition between andesine and bytownite exhibits hues ranging from colourless to light yellow on the smaller stones to champagne or straw yellow on the largest.
The variety known as ‘rainbow moonstone’ exhibits multi-coloured sheen. Semi-transparent blue and multi-coloured sheen moonstone from Patna, Bihar, India (RI 1.56; SG 2.69) marketed as ‘Blue Rainbow’ moonstone
and ‘Rainbow‘ moonstone may be either labradorite or bytownite.
The finest stones have a reddish orange or sometimes a lavender sheen with areas of green and blue. The colour effects shown by rainbow moonstone from India arise due to diffraction from intergrowths of repeated twin lamellae and not from exsolution. They appear white to almost colourless because they lack the ilmenite inclusions that give most labradorite a dark greyish body.
Black moonstone
Name given to colourless labradorite (anorthosite) which exhibits only sporadic bluish labradorescence and is darkened by needle-like inclusions, that give some degree of chatoyancy when appropriately cut. However, the name has also been applied to material from Myanmar (formerly known as Burma) that shows a similar effect to moonstone but with more ‘play of colour’ (SG 2.69).
Bull’s eye
Name sometimes applied to relatively dark labradorite (anorthosite).
Lynx eye
Labradorite with a predominantly green iridescence.
Opaline feldspar
Name sometimes given labradorite from anorthosites.
Ox-eye
Name sometimes applied to labradorite (from anorthosites) that exhibits dark reddish hues.