Where the name comes from

Labradorite was named after the Labrador Peninsula of Canada, where striking iridescent feldspar was described in the late 1700s. It sits near the middle of the plagioclase series (between sodium‑rich albite and calcium‑rich anorthite).

What it is (in one breath)

A triclinic feldspar with two near‑right‑angle cleavages, characteristic polysynthetic twinning that can show as fine striations, and—when conditions are just right—those famous color flashes from nanoscale layering inside the crystal.

Igneous roots

Labradorite crystallizes from mafic to intermediate magmas and is common in gabbro, basalt, and norite. In some intrusions, it builds almost monomineralic rocks called anorthosites—vast feldspar bodies with planetary vibes (the Moon’s highlands are anorthositic, too).

Slow color recipe

As the crystal cools, slight differences in composition (Na–Ca zoning) separate into ultra‑thin lamellae. This exsolution texture sets the stage for interference colors later—the physical basis of labradorescence.

Metamorphic cameos

Labradorite also appears in metagabbros and amphibolites, where original igneous feldspar survives or re‑equilibrates during metamorphism, sometimes sharpening the internal lamellae that produce color.

Physics, friendly version

Inside labradorite, ultra‑thin layers (tens to hundreds of nanometers) with slightly different refractive indices act like a tiny, orderly stack of mirrors. Light reflecting between them interferes—amplifying some colors and canceling others. The result: broad, neon‑like sheets of blue, green, gold, or orange that appear when light strikes at the right angle.

Why angle matters

The lamellae lie along specific crystallographic planes (often near a cleavage). If a surface intersects those planes just so, color blooms; tilt away and it fades. That’s why cabochons are oriented to “find” the strongest flash.

At‑home demo: Hold a stone under a small lamp and rock it slowly. When color ignites, note the direction of the flash relative to any visible striations—your personal map to its internal layers.

Cabochon surfaces

At 10× you may see faint parallel lines or zones under the polish. The color sheet appears “behind” the surface, moving as you tilt—evidence of internal interference layers rather than a surface coating.

Thin sections

• Distinct polysynthetic twins (zebra stripes) in crossed polars.
• 1^st‑order interference colors (grays/yellows) except where alteration occurs.
• Lamellar microstructure responsible for iridescence may be below optical resolution.

Alteration textures

Fine sericitization (mica‑like alteration) along cleavages and clouds of tiny inclusions can soften transparency in non‑gemmy pieces—often part of the stone’s rugged charm.

Spectrolite (Finland)

A term popularized for exceptionally vivid, full‑spectrum labradorescence—from electric blues to greens, golds, oranges, and purples—often found in dark, unaltered material from Finland.

Andesine–Labradorite

Plagioclase composition ranges smoothly. “Andesine” (more Na) and “labradorite” (more Ca) meet in the middle; both can show iridescence, though labradorite is the classic flash bearer.

Sunstone (plagioclase with aventurescence)

Another plagioclase phenomenon: aventurescence, a glitter from tiny copper platelets or hematite—not the broad color sheets of labradorescence. Oregon sunstone is a famous example.

Classic & widely seen

Canada (Labrador, Newfoundland), Madagascar, and India produce abundant material in a range of flashes. Large decorative slabs often come from Madagascar.

Other appearances

Finland (spectrolite), Norway, Russia, Ukraine, and the USA (Oregon, New York) among others. Geological neighbors include anorthosite massifs and mafic intrusions.

Moonstone (orthoclase)

Shows a soft adularescence—a floating glow—rather than broad, vibrant color sheets. Moonstone is usually paler and often exhibits a single, centered sheen.

Opal & coated quartz

Opal’s play‑of‑color is patchy and granular at high magnification; coated “mystic” quartz shows surface iridescence (rainbow on every facet). Labradorite’s color lives inside and is directional.

Rainbow obsidian / glass

Volcanic glass lacks cleavage and twinning striations; its sheen is banded and concentric. Labradorite will show feldspar’s twin lines and right‑angle cleavages under light.

Hawk’s‑eye / tiger’s‑eye

Quartz pseudomorphs with fibrous sheen (chatoyancy) forming stripes, not sheets. Very different under a loupe.

Quick checklist

• Two near‑right‑angle cleavages; glassy luster.
• Fine parallel striations on certain faces (plagioclase twins).
• Flash appears and disappears strongly with angle—broad sheets of color.

What not to do

Scratching or acid testing isn’t necessary. Observation, rotation, and a hand lens tell the story gently.

Everyday handling

• Hardness around 6–6.5 resists casual wear, but cleavage means avoid sharp blows.
• Wipe with a soft cloth before viewing—the flash loves a clean surface.

Cleaning

• Lukewarm water + mild soap + soft brush; rinse and dry.
• Avoid ultrasonic/steam for stones with visible fractures or heavy internal stress.

Display & photo tips

• Side‑light at ~30° and a white bounce card opposite the light make color leap out.
• Rotate slowly and note the angle where the flash peaks; that’s your “hero” pose.