Labradorescence is a play-of-colorgem phenomenon that occurs in gem quality labradorite. The phenomenon results from reflection of light from the layers of thin plates (lamellar) arrangement within the stone. When that arrangement causes polarization the labradorite appears blue.
Labradorite, Gold and Enamel Stickpin Depicting Bacchus, c. 1890.
Photo Courtesy of Christie’s.