Spectrolite

Spectrolite is a trade name for an exceptional variety of labradorite, a calcium-sodium plagioclase feldspar. It is distinguished from ordinary labradorite by its dark, often nearly black body color and its ability to flash the entire visible spectrum, including reds, oranges, and yellows that are rare in typical labradorite.

The name was coined in Finland, where the gem was discovered near Ylamaa during World War II. Finnish spectrolite remains the benchmark for the material, though similar high-quality labradorite is occasionally marketed under the name.

The striking optical effect, called labradorescence, arises from light interference within the feldspar's microscopic internal layering, producing vivid metallic-looking sheens that shift as the stone is turned.

Spectrolite forms as a plagioclase feldspar within slowly cooled mafic igneous rocks such as anorthosite and gabbro. As the magma crystallizes, the feldspar develops fine alternating lamellae of slightly different composition (exsolution lamellae), and it is the interference of light from these submicroscopic layers that creates labradorescence.

The finest spectrolite comes from the Ylamaa region of southeastern Finland, where it occurs in anorthositic rocks. Labradorite displaying strong, broad-spectrum flash is also found in Madagascar, Canada (Labrador, the original source), and elsewhere, though the dark-body, full-spectrum Finnish material set the standard for the spectrolite name.

Spectrolite is recognized by a dark gray-to-black base that erupts into bright iridescent flashes spanning the full spectrum, including reds and golds, when viewed at the right angle. Hardness is about 6-6.5, and it shows the two good cleavage directions typical of feldspar.

The iridescence is directional: it appears as broad sheets of color that vanish and reappear as the stone tilts, unlike the surface-only play of cheap imitations. Luster is vitreous to slightly pearly on cleavage surfaces.

Distinguish it from ordinary labradorite (paler body, usually only blue-green flash) and from moonstone (adularescent billowy white-blue glow rather than spectral flash). Glass imitations lack true cleavage and internal layering.

Spectrolite is used almost exclusively as a gemstone and ornamental material. It is cut into cabochons, beads, and freeform shapes for rings, pendants, and statement jewelry, and larger pieces are fashioned into carvings and decorative objects.

Its value depends on the strength, breadth, and coverage of the color flash, with stones showing strong red and gold flashes against a dark body commanding premiums. Finnish-origin material is especially prized.

In metaphysical practice spectrolite is regarded, like labradorite, as a stone of transformation, protection, and intuition; these associations are traditional beliefs rather than scientifically established properties.