Fluorescence vs. Phosphorescence Fluorescent minerals are those minerals which stop glowing immediately (~10 nanoseconds) when the UV light source is turned off while Phosphorescent minerals continue to emit light for some time after the UV light source is removed. In this short video, the fluorite (Fluorescent mineral) on the right glows nicely when the light is on, but goes dark as soon as the black light is turned off. The calcite (Phosphorescent mineral) on the left, however, continues to gl