Authenticating Labradorite: Formation, Testing & Quality
Geography & Geological Formation
Labradorite is found in several regions around the world, with notable deposits in Canada, Finland, Madagascar and Russia. Each location contributes to the gem's diversity in quality and appearance, adding to its global appeal.
Canada
The most famous labradorite deposits are found in Labrador, Canada, where the stone was first discovered. The deposits in this region are rich in high-quality specimens exhibiting vibrant labradorescence. In Newfoundland, another Canadian province, labradorite is also mined and often showcases exceptional colour play.
Finland
In Finland, a unique variety of labradorite called Spectrolite is found. Discovered during World War II, Spectrolite is known for its intense, broad spectrum of colours, including blues, greens, yellows, and oranges. The stones from this region are particularly prized for their vivid and complete colour display.
Madagascar
Madagascar is another significant source of labradorite, providing stones with a wide range of colours. The labradorite from Madagascar often has a striking blue or green labradorescence and is highly sought after in the gem market.
Russia
In Russia, labradorite is found in the Ural Mountains. Russian labradorite can display a rich array of colours and is known for its high quality. These stones are used in both jewellery and ornamental pieces.
Image: Ural Mountains, Russia
GEOLOGICAL FORMATION
Labradorite forms in igneous rocks, specifically in basalt, gabbro, and anorthosite. These rocks originate deep within the Earth's crust and are formed from magma that cools and solidifies.
The formation of labradorite begins deep within the Earth's crust, where high-temperature and high-pressure conditions are prevalent. As magma cools, minerals begin to crystallise. Labradorite crystals form when calcium-rich plagioclase feldspar solidifies.
The unique play of colour, or labradorescence, occurs due to the presence of twinning planes within the crystal structure. These planes cause light to scatter and create the stone's characteristic iridescent effect.
The Wider Feldspar Family
The diagram below shows the breakdown of feldspar varieties:
Chemical Composition & Colouring
Labradorite is part of the plagioclase feldspar family, with a chemical composition of (Ca,Na)(Al,Si)₄O₈. It contains a mix of calcium and sodium aluminosilicates and small amounts of potassium feldspar. The balance of these elements within the crystal structure significantly influences its visual properties.
Inside labradorite, thin, parallel layers called twinning planes are critical to its colourful appearance. These twinning planes occur when the crystal grows in such a way that one part becomes a mirror image of the other. In labradorite, these planes are very fine and numerous.
Labradorescence is the name given to the vibrant flashes of colour seen in labradorite. This effect occurs due to the interference of light within the crystal. When light enters the stone, it hits the twinning planes and is scattered. The scattered light waves interfere with each other, causing the spectacular flashes of colour that characterise labradorite. The colours observed change with the angle of light and the viewer's perspective, making the labradorite a dynamic and ever-changing gemstone.
Image: © 2025 Candice Hamilton, The Spiritual Gemmologist. All rights reserved. No unauthorised use or reproduction.
Causes of Iridescence
Iridescence, which includes labradorescence, can be caused by the diffraction (bending) of light from regular structures or by reflection from thin films within the material. In labradorite, both these factors are at play:
Diffraction of Light: The fine layers within the crystal act like a diffraction grating, breaking up the light into its component colours. This is similar to how a CD or soap bubble shows a rainbow of colours.
Thin Film Interference: Light hitting thin layers within the crystal is partly reflected from the upper surface and partly from the lower surface. These reflections can interfere with each other, either amplifying or cancelling out certain colours. When the light waves are in phase (peaks and troughs align), the colours become brighter. When they are out of phase (peaks align with troughs), the colours are diminished or eliminated.
Image: © 2025 Candice Hamilton, The Spiritual Gemmologist. All rights reserved. No unauthorised use or reproduction.
Colour Ranges
Labradorescence can produce a wide range of colours depending on the thickness and spacing of the twinning planes:
Blues and Greens: These are the most common and vibrant colours seen in labradorite. They result from thinner twinning planes that scatter light more effectively.
Gold and Yellow: Less common but highly sought after, these colours are produced by slightly thicker twinning planes.
Orange and Red: Rare and highly desirable, these colours appear in very high-quality specimens and result from even thicker twinning planes.
Purple and Pink: Extremely rare, these colours occur under specific conditions within the crystal structure and are usually only seen in the finest specimens.
Identification Of Labradorite
SUGGESTED TESTING METHODS
We recommend using the following standard gemmological tools and methods to determine authenticity:
OBSERVATION
Look for it’s unique iridescence, known as labradorescence, which displays flashes of blue, green, yellow, and sometimes pink, red or purple. Look for natural inclusions, fractures, or internal cracks. Examine the stone for transparency. Labradorite can range from translucentA material that allows some light to pass through it, but not enough to see objects clearly on the other side. Translucent gems let light in but diffuse it, making them appear foggy or blurry when you try to look through them.
to
opaqueA material that does not allow any light to pass through, making it impossible to see through the gem., and typically has a milky or cloudy appearance. High quality labradorite will be more translucent. It’s external texture is granular and will display two distinct cleavage planes.
Image: Iridescent colours in labradorite
Image: Iridescent colours in labradorite
LOUPE (OR MICROSCOPE)
Examine the cleavageCleavage refers to the tendency of a gemstone to break or split along specific planes of weakness within its crystal structure. These planes are areas where the bonds between atoms are weaker, making it easier for the gem to break along those lines. planes more closely. Labradorite often shows two directions of perfect cleavage at nearly right angles (at 90 dregrees), which can be seen as parallel lines or steps on broken surfaces. Natural labradorite will have a slightly uneven, sometimes granular texture, especially in unpolished areas.
SPECIFIC GRAVITY
Specific gravity (SG) is a measure of the densityDensity refers to how much mass it has in a given volume. It's a measure of how heavy a gem feels for its size. For example, if two gems are the same size but one feels heavier, the heavier one has a higher density. of a mineral compared to the density of water. For labradorite, the specific gravity typically ranges from 2.68 to 2.72. A significant deviation might indicate a different material. This can be measured using a hydrostatic balance.
REFRACTOMETER
The refractive index (RI) of labradorite usually ranges from 1.559 to 1.570. Translucent pieces work best for testing. Samples with smooth, polished surfaces are ideal because they give more accurate readings. Labradorite is an anisotropicA material that has different optical properties depending on the direction of the light passing through it. Anisotropic gems can show different colours when rotated under polarised light. biaxial A type of anisotropic gem that has two different optical axes. When light enters a biaxial gem, it can split into two rays, each behaving differently. These gems can have more complex optical effects. material which means when using the refractometer, you should see two shadow edges and both of them will move so be sure to test with carefully.
DESTRUCTIVE TESTING
Destructive testing refers to methods that evaluate a gemstone's properties, authenticity, and treatments by causing irreversible damage to the sample. Destructive testing is not recommended and should only be carried out as a last resort. Do not conduct destructive testing on valuable items, items that you don’t own or without the owner’s permission to do so.
Hardness Test: Labradorite can be scratched by items like a steel nail or a piece of quartz, confirming its hardness of 6 to 6.5 on the Mohs scale.
Labradorite Gallery
Other Varieties of Labradorite
SPECTROLITE
This gemstone is a rare variety of labradorite found exclusively in Finland. It boasts a stunning play of colours unlike most other labradorites. Spectrolite exhibits a vivid spectrum of colours, often including blues, greens, and golds, against a darker background. Spectrolite's unique beauty and limited source make it a highly sought-after gemstone prized for jewellery and decorative purposes.
RAINBOW MOONSTONE
While the name might suggest a connection to moonstone, rainbow moonstone is actually a variety of labradorite. Unlike the typical labradorite with its play of blues and greys, rainbow moonstone showcases a white body with a blue iridescence that resembles the adularescent sheen found in moonstone. This effect is likely due to a higher albite content within the labradorite's composition.
NOTE: It’s worth pointing out that moonstone is considered a different variety of orthoclase feldspar and is different to rainbow moonstone.
Enhancements & Artificial Materials
Labradorite typically does not require enhancements or is subjected to treatments. Labradorite also isn’t typically imitated by other materials since it’s an abundant and affordable material with unique optical properties.
labradorite buying guide
HIGHER QUALITY
Colour: Exhibits vibrant and strong colours. The colours can range from blue, green, and gold to rarer colours like red and purple.
Condition: High-quality labradorite has a smooth, polished surface with minimal surface blemishes or fractures.
Transparency: Often semi-translucent to translucent. This enhances its colour and overall appearance. higher quality
LOWER QUALITY
Colour: Weak or absent of colours. The stone may appear dull or have a muddy colour.
Condition: Lower quality labradorite may have a rough or uneven surface, with visible fractures, chips, or scratches.
Transparency: Lower quality labradorite tends to be opaque or have significant inclusions.
