What is the term for the broad color flash seen in certain gems?

The term for the broad color flash seen in certain gems is known as labradorescence. This phenomenon occurs in minerals that exhibit a play of color, specifically in labradorite and some related feldspars. Labradorescence is characterized by an optical effect that produces a vibrant range of colors, sometimes including blues, greens, and golds, that shift and change with the angle of viewing and the light source. This effect arises from the internal microstructure of the mineral, which causes light to scatter and refract in various ways, creating the distinct flashes of color.

Other terms listed, such as adularescence, schiller, and the cat's eye effect, refer to different optical phenomena observed in specific gemstones. Adularescence, for example, is a soft, shimmering light seen in stones like moonstone, while schiller typically describes a metallic sheen in certain types of feldspar or other minerals. The cat's eye effect is an optical illusion seen in certain gemstones, like chrysoberyl, where a band of light appears to move across the surface. Each of these phenomena showcases unique characteristics and does not represent the broad color flash associated with labradorescence.