What is Fluorescence in Minerals?

Some minerals exhibit a property known as fluorescence, where they emit visible light after being exposed to ultraviolet (UV) radiation.

Ultraviolet light is electromagnetic radiation with a wavelength shorter than visible light, typically between 100 - 400 nanometers. It’s not visible to the human eye but carries enough energy to excite electrons in certain materials.

When UV photons strike a fluorescent mineral, the atoms inside the crystal lattice absorb this energy. Electrons are excited to a higher energy state. Almost instantly, those electrons drop back down to their original state, releasing the excess energy as photons of visible light.

The color of the fluorescence depends on the composition of the mineral, particularly the presence of activator ions or trace impurities (like manganese, uranium, lead, rare-earth elements). For example, manganese often produces red or pink fluorescence in calcite, while uranium can cause a greenish glow in autunite.

Not every mineral fluoresces because most crystal structures allow absorbed energy to dissipate as heat instead of re-emitting it as visible light.

Fluorescence is a very short-lived process (on the scale of nanoseconds). As soon as the UV source is removed, the glow stops immediately. This distinguishes it from phosphorescence, where the glow can persist after the excitation source is gone.

Facts About Fluorescent Minerals

• Only about 15% of all minerals can fluoresce.
• Some minerals can fluoresce in different colors under shortwave UV and longwave UV.
• Fluorescence is sometimes used by geologists and miners to identify minerals quickly.

Examples of Fluorescent Minerals