A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure and specific physical properties. A rock, by comparison, is an aggregate of minerals and need not have a specific chemical composition. Minerals range in composition from pure elements and simple salts to very complex silicates with thousands of known forms.
Fluorescence is a luminescence that is mostly found as an optical phenomenon in cold bodies, in which the molecular absorption of a photon triggers the emission of another photon with a longer wavelength. The energy difference between the absorbed and emitted photons ends up as molecular vibrations or heat. Usually the absorbed photon is in the ultraviolet range, and the emitted light is in the visible range, but this depends on the absorbance curve and Stokes Shift of the particular fluorophore. Fluorescence was coined by George Gabriel Stokes in his 1852 paper, the name was given as a description of the essence of the mineral fluorite, composed of calcium fluoride, which gave a visible emission when illuminated with UV radiation.
Calcite (Red/Orange), Willemite (Green), Zincite and Franklinite are some of the minerals contained in the above specimen on display, in Franklin Mineral Museum. With about 380 different minerals (out of the nearly 3800 known to mankind) - many of them adorning the showcases of Sterling Hill Mining Museum and Franklin Mineral Museum - this region is aptly known as the Fluorescence Capital of the World.
