Fluorite or Fluorspar is a mineral composed of calcium fluoride (CaF2), the principal fluorine-bearing mineral. It occurs as cubic, isometric crystals and cleavable masses. When pure, it is colorless and transparent, or translucent with a glassy luster. Impurities cause color in the stone, and several varieties exhibit fluorescence. Usually found either in pure veins or associated with lead, silver, or zinc ores, it is common in limestone and dolomites. Fluorite occurs in England and the United States. Fluorite comes in a wide range of colors and has subsequently been dubbed "the most colorful mineral in the world". The most common colors are purple, blue, green, yellow, or colorless. Less common are pink, red, white, brown, black, and nearly every shade in between. Color zoning or banding is commonly present. The color of the fluorite is determined by factors including impurities, exposure to radiation, and the size of the color centers.