A proprietary name for labradorite from Finland that exhibits exceptionally strong play of colour. Discovered in 1940 during construction of a defensive line in southeastern Finland, in the middle of the Second World War.

Thin layers of feldspar within the stone interfere with light, producing a full spectral display. Labradorite occurs worldwide, but specimens showing the complete rainbow are concentrated in Finland's Ylämaa region.

A wartime accident of discovery gave one mineral its own proper noun. Beneath the feet of soldiers digging trenches, a rainbow.