Fluorescence
Definition
The emission of visible light by a mineral when exposed to ultraviolet (UV) light. The light stops when the UV source is removed.
Example
Many fluorite specimens glow blue or green under UV light.
Glowing in the Dark
Fluorescence is the emission of visible light by a substance that has absorbed light or other electromagnetic radiation (usually Ultraviolet or "Black Light"). The emitted light has a longer wavelength (lower energy) than the absorbed radiation. The effect creates an eerie, neon-like glow that disappears the instant the UV source is turned off. If the glow persists, it is called <strong>phosphorescence</strong>.
Causes and Chemistry
The glow is caused by "activator" elements—impurities like manganese, lead, or rare earth elements—within the crystal lattice. Other elements, like iron, act as "quenchers" and prevent fluorescence. The most famous fluorescent mineral locality is Franklin, New Jersey, where Calcite glows red and Willemite glows green.