Ulexite, sometimes known as TV rock, is a mineral occurring in silky white rounded crystalline masses or in parallel fibers. The natural fibers of ulexite conduct light along their long axes, by internal reflection.
Ulexite was named for the German chemist Georg Ludwig Ulex (1811–1883) who first discovered it. It is found principally in California and Nevada; Tarapacá Region in Chile, and Kazakhstan.
Ulexite is also known as TV rock due to its unusual optical characteristics. The fibers of ulexite act as optical fibers, transmitting light along their lengths by internal reflection. When a piece of ulexite is cut with flat polished faces perpendicular to the orientation of the fibers, a good-quality specimen will display an image of whatever surface is adjacent to its other side. The fiber-optic effect is the result of the polarization of light into slow and fast rays within each fiber, the internal reflection of the slow ray and the refraction of the fast ray into the slow ray of an adjacent fiber.
Here is a photo of a silver ring with created green ulexite: