Gem library
Labradorite
The feldspar of blue lightning
Labradorite is a dull grey feldspar that, at the right angle, catches fire in blue, green, gold and violet flashes. That phenomenon — labradorescence — is not a colour but light interference on internal lamellae a few hundred nanometres thick.
- Hardness (Mohs)
- 6 – 6.5
- Density
- 2.68 – 2.72
- Crystal system
- Triclinic
- Refractive index
- 1.559 – 1.573
- Cleavage
- Perfect on {001}, distinct on {010}
Mineralogical identity
- Family
- Plagioclase feldspars
- Species
- Labradorite
- Variety
- Spectrolite (Finland)
- Chemical formula
- (Ca,Na)(Al,Si)₄O₈ — 50 to 70 % anorthite
- Crystal system
- Triclinic
- Classification
- Semi-precious stone
- Rarity
- Common
- Indicative price
- €0.50 – 15/ct
Etymology
From Labrador, Canada, where Moravian missionaries found it in 1770 on Paul Island.
Physical & optical properties
- Hardness (Mohs)
- 6 – 6.5
- Density
- 2.68 – 2.72
- Refractive index
- 1.559 – 1.573
- Birefringence
- 0.008 – 0.010
- Cleavage
- Perfect on {001}, distinct on {010}
- Fracture
- Splintery
- Lustre
- Vitreous, labradorescent
- Diaphaneity
- Translucent to opaque
- UV fluorescence
- None
- Pleochroism
- None
- Colours
- grey, multicoloured, blue, gold, purple
Formation, geology & history
The physics of labradorescence
Inside the crystal, unmixing has separated the material into alternating lamellae of slightly different composition — the Bøggild exsolution lamellae. Their thickness, of the order of 100 to 300 nanometres, matches the wavelengths of visible light: rays reflected by successive layers interfere and return a specific colour. The thinner the lamellae, the more the colour leans blue and violet; the thicker, towards gold and red. The effect is directional: it appears only within a precise angular cone, which forces the lapidary to orient the stone with care. A badly oriented labradorite stays hopelessly grey.
Spectrolite and varieties
Finnish spectrolite, discovered during the building of fortifications in 1940, shows labradorescence across the whole spectrum, including red and orange, on a deep black ground. It is the most prized variety. Madagascar supplies most of the world market, with brilliant blues and greens. Transparent yellow labradorite from Mexico and Oregon (sometimes called Oregon sunstone when it contains copper platelets) is facetable and worth considerably more. Finally, the commercial «rainbow moonstone» is in fact a translucent white labradorite, not to be confused with true moonstone (orthoclase).
A building rock
Labradorite forms entire masses in gabbros and anorthosites, those deep magmatic rocks. In Madagascar it is quarried in blocks of several tonnes, sliced into slabs for decoration and funerary work. The collector market is mainly interested in polished plates with strong labradorescence and in cabochons. In jewellery it needs a protective setting: its double cleavage makes it brittle and it chips easily during mounting.
How to recognise it
- A flash that appears then vanishesTilt the stone slowly: the colour must burst out suddenly within a precise angle, then die away. A permanent sheen betrays iridised glass or a coating.
- Dull grey ground outside the angleA labradorite that stays coloured from every angle is suspect. The contrast between the base grey and the blaze is its signature.
- Pearly cleavage planesFlat shiny facets appear on the edges: typical of feldspars.
Imitations, treatments & confusions
- Iridised glass («aura» and dichroic glasses)Permanent, over-uniform coloured reflections, often in thin vacuum-deposited layers. The glass warms fast in the hand and shows no cleavage.
- Metal-coated stone«Angel aura» quartz and similar are coated with a vaporised layer of titanium or gold. The iridescence is uniform and superficial, very different from labradorescence in depth.
- Confusion with moonstoneThe trade's rainbow moonstone is a white labradorite. Not a fake but a misleading name: true moonstone is an orthoclase with milky adularescence.
Deposits & origins
Madagascar (the largest world producer, blocks with strong labradorescence), Finland (Ylämaa spectrolite, the most colourful), Canada (Labrador, the historic deposit), Russia (Ukraine and Karelia), Mexico, Australia, Norway
Care & precautions
- Brief rinsing in warm soapy water, gentle drying. Avoid prolonged soaking.
- Insensitive to sunlight, unlike many coloured stones.
- Sensitive to impact because of the double cleavage: store it separately and avoid heavily exposed rings.
- No ultrasonic cleaning or steam, which risk opening the cleavage planes.
Traditions & crystal healing
- Chakras
- Third eye · throat
- Zodiac signs
- Leo · Scorpio · Sagittarius
- Element
- Water · Air
Tradition makes it a discreet shield: it is said to protect from outside influences while revealing inner resources — the brilliance hidden beneath the grey. It is often presented as the stone of transitional periods and of caring professions, to be kept on the person rather than displayed.
The virtues described here belong to tradition and cultural heritage. They are in no way medical advice and never replace a consultation.
Frequently asked questions
Why doesn't my labradorite flash?
Because labradorescence is directional: it appears only within a precise angular cone. Tilt the stone slowly under a point light until you find the angle.
Labradorite or moonstone?
Labradorite throws vivid blue and green flashes on a grey ground; moonstone (orthoclase) has a milky bluish veil floating inside. The trade's rainbow moonstone is actually a labradorite.
What is spectrolite?
A Finnish labradorite whose labradorescence covers the whole spectrum, into red and orange, on a black ground. It is the rarest and most expensive variety.