Labradorite – natural minerals and polished stones

Labradorite – a feldspar mineral renowned for its remarkable labradorescence

Labradorite is a calcium-sodium member of the plagioclase feldspar series, distinguished by the unique optical phenomenon known as labradorescence. When illuminated from the proper angle, its surface displays vivid blue, green, turquoise, gold, orange and even multicolored flashes. The underlying body color of the mineral is typically gray, gray-green, whitish or nearly black.

Labradorite belongs to the plagioclase feldspar group and has a chemical composition intermediate between sodium-rich albite and calcium-rich anorthite. The name labradorite generally refers to plagioclase containing approximately 50–70% anorthite. Its generalized chemical formula is expressed as (Ca,Na)(Al,Si)₄O₈.

The most valuable specimens display strong, broad areas of labradorescence and a clean surface free from deep fractures. Labradorite is commonly fashioned into cabochons, beads, pendants, bracelets, polished freeforms and decorative objects. Rough crystals, cleavage blocks and specimens preserved in their host rock are also highly prized by mineral collectors.

How Labradorite forms

Labradorite forms primarily through the crystallization of magma in mafic and intermediate igneous rocks. It is a common constituent of gabbro, norite, basalt, anorthosite and certain diorites. It may also occur in metamorphic rocks that have undergone transformation under elevated temperatures and pressures.

As originally homogeneous plagioclase cools, microscopic lamellae with slightly different chemical compositions separate within the crystal. These extremely thin alternating layers refract, scatter and interfere with incoming light, producing the characteristic optical effect visible only from certain viewing angles.

The intensity of labradorescence depends on the thickness and regularity of the lamellae, the orientation of the cut, the clarity of the material and the viewing angle. Poorly oriented cutting may leave even high-quality rough appearing dull and gray, whereas correctly oriented material reveals broad, vivid flashes of color. Experienced lapidaries therefore carefully determine the direction of the strongest optical effect before cutting.

What is labradorescence?

Labradorescence is not a surface coating or pigmentation. It is an internal optical phenomenon caused by the interference of light within microscopic lamellae inside the plagioclase crystal. As a result, the colorful flashes change depending on the orientation of the stone, the direction of illumination and the observer's position.

Blue and blue-green reflections are the most common, although exceptional material may also display gold, yellow, orange, pink and violet colors. Labradorite showing an especially broad spectrum of colors is sometimes marketed under the trade name Spectrolite. Originally, this name referred specifically to premium-quality Finnish labradorite with exceptionally intense multicolored effects.

Labradorescence is sometimes confused with adularescence, the optical effect characteristic of moonstone. Adularescence usually appears as a soft bluish-white glow, whereas labradorescence produces sharper, brighter and much more vividly colored flashes.

Major Labradorite localities

Labradorite occurs on several continents, but deposits differ considerably in the intensity of their color flashes, the size of colorful areas, transparency and overall gemstone quality.

• Canada: Labradorite was first described from the Labrador Peninsula, where it became known during the 18th century. Canadian material commonly exhibits blue, green and golden flashes.
• Madagascar: One of today's most important producers of gem-quality and ornamental labradorite. Material from Madagascar often displays striking blue, green, gold and multicolored labradorescence.
• Finland: The Ylämaa deposit is famous for producing Spectrolite, characterized by exceptionally vivid and broad multicolored optical effects.
• Ukraine: Labradorite and labradorite-bearing rocks occur in large blocks and are widely used as decorative building stone.
• Russia, Norway, Mexico, the United States, Australia and India: Additional important sources of labradorite and plagioclase-rich rocks.