The Schiller Effect is an optical effect whereby light appears to originate from beneath the surface of a stone. This effect arises in minerals composed of stacked layers that are slightly ‘out-of-sync’. Some waves of light collide with the first layer, immediately reflecting back, while others make it past the first layer only to be reflected by the next. This continues resulting in multiple waves that can constructively or destructively interfere with one another, generating a multi-layered, sometimes multi-colored, milky appearance.
This term is often used synonymously with adularescence, aventurescence, or labradorescence although it is more appropriate to consider these three as subcategories of the Schiller effect. The Schiller effect materializes in stones spanning Moonstone, Tiger Eye, and Labradorite.