Labradorite ((Ca,Na)(Al,Si)₄O₈) is one of the more common minerals found in the upper part of the Earth’s crust. It belongs to the feldspar group, whose members are important rock-forming minerals in numerous igneous rocks worldwide.
In Finland, however, a special variety of labradorite occurs that displays a striking optical phenomenon known as labradorescence. Light is refracted and interferes within thin lamellae in the mineral’s internal structure, producing characteristic iridescent colours on the stone’s surface. Blue and green reflections are the most common, while specimens displaying the full spectrum of rainbow colours are the rarest and therefore especially prized.
The gem-quality variety of labradorite with exceptionally vivid labradorescence is known as spectrolite. Its most important occurrence is in Finland. Significant deposits of labradorite are also found in Canada, home to the famous Labrador region from which the mineral derives its name, and in Madagascar, which today supplies a large share of the specimens available on the market.
The zonal structure of a Finnish labradorite crystal reveals the characteristic play of colours for which spectrolite is so highly valued. Photo: Boštjan Burger
