Fluorite

Fluorite is a vitreous and translucent mineral, available in a wide range of colors (green, purple, blue, yellow, and colorless) due to impurities of iron and other elements. Its cubic crystal structure makes it easily recognizable. It is mainly found in China, Mexico, and England, and has been used since antiquity as a decorative stone and to reduce the viscosity of molten metals (hence its name, from the Latin 'fluere', to flow). Alchemists associated it with transmutation due to its ability to fluoresce under UV light.