What Is Labradorite? The Physics Behind Its Flash
Labradorite is a feldspar mineral in the plagioclase group, first formally described from Labrador, Canada, in the late 18th century — hence the name. Its signature effect, labradorescence, is a flash of vivid color that appears and disappears sharply as the stone is tilted.
The Physics of Labradorescence
Like moonstone, labradorite's optical effect comes from internal layering formed through exsolution as the mineral cooled slowly underground — but the layers in labradorite are thinner and more regularly spaced, close to the wavelength of visible light. Light reflecting off these evenly-spaced internal layers interferes with itself (similar to thin-film interference, the same physical principle behind the colors in a soap bubble or an oil slick), reinforcing specific wavelengths depending on the exact layer spacing and viewing angle — which is why the flash appears as sharp, specific colors rather than a soft overall glow, and why it shifts abruptly rather than gradually.
Grading and "Spectrolite"
Labradorite is graded largely on the strength and color range of its flash — material showing a full spectrum of colors across a large surface area commands significantly more than material with a weak, single-color flash confined to a small area. The most vivid material, showing a wide range of intense colors, is often marketed under the trade name spectrolite, historically associated with Finnish material discovered in the 1940s.
Where It's Mined
Madagascar and Finland are the two most significant sources of fine labradorite, with Finland specifically known for spectrolite-grade material. Additional deposits exist in Canada (including the original Labrador locality) and parts of the United States.
Quick Facts
Mineral family: feldspar (plagioclase group) — Hardness: 6–6.5 on the Mohs scale — Optical effect: labradorescence, from thin-film interference in exsolution layers — Finest material sometimes marketed as spectrolite — Major sources: Madagascar, Finland.