Some minerals will emit light when they are activated by an energy form other than visible light. We call such an effect luminescence. Examples of luminescence include fluorescence, phosphorescence, and thermoluminescence.
This photo is a fluorescent specimen from the Franklin Mine in New Jersey. It is illuminated with short wavelength ultraviolet light and contains green willemite (Zn2SiO4), blue hardystonite (Ca2ZnSi2O7), orange clinohedrite (CaZnSiO4•H2O), and minor red calcite (CaCO3). Fluorescent minerals like the ones seen here give off visible light when they are struck by energy with wavelength shorter than visible light. If the visible emission continues after the energy source is turned off, the mineral is phosphorescent. Pectolite is an example of a phosphorescent mineral.
Thermoluminescent minerals, such as some tourmalines, give off visible light in response to heating. Some varieties of fluorite, calcite, and apatite also have this property.