Labradorite

Labradorite is a member of the plagioclase feldspar series, an aluminosilicate of calcium and sodium. While its base color is an unassuming gray, it is renowned for a spectacular optical effect called labradorescence—broad flashes of iridescent blue, green, gold, and occasionally orange and violet that shift as the stone is turned.

This schiller effect is caused by light interference within fine internal layering (exsolution lamellae) in the crystal. The most intensely multicolored variety, from Finland, is called spectrolite.

First described from Labrador, Canada, labradorite is both a rock-forming mineral and a popular gemstone.

Labradorite is a common rock-forming mineral that crystallizes from cooling magma, especially in mafic igneous rocks such as basalt, gabbro, and anorthosite. The internal lamellae responsible for its color flash form as the feldspar slowly cools and separates (exsolves) into alternating microscopic layers.

Large anorthosite bodies are major sources of gem labradorite. It also occurs in some metamorphic rocks.

Key localities include Labrador and Quebec (Canada), Finland (spectrolite), Madagascar, and Russia (Ukraine's Volyn region historically).

• Labradorescence: The defining clue—turn the stone and watch for sheets of blue/green/gold flash that appear and vanish at certain angles.
• Base color: Dark gray to smoky, sometimes translucent.
• Hardness: 6-6.5; just below quartz.
• Cleavage: Two good cleavage directions at nearly 90 degrees (typical of feldspar), often visible as flat reflective surfaces.

Look-alikes: Moonstone (also feldspar) shows a softer billowy white-blue adularescence rather than the bold colored flash. Spectrolite is simply top-grade labradorite. Imitation glass 'flash' is too uniform and lacks the angle-dependent sheen.

Labradorite is a popular gemstone, cut into cabochons, beads, and carvings that showcase its flash, and used in pendants, rings, and ornamental objects. Spectrolite commands premium prices for its vivid full-spectrum play of color.

As a rock-forming feldspar, the broader plagioclase group is geologically important and crushed feldspar has industrial uses in glass and ceramics.

Value depends on the strength, color range, and coverage of the labradorescence. Metaphysically it is associated with intuition and transformation—cultural belief, not science.