Mineral Guide > Gems > Phosphorescence of Gems

Phosphorescence of Gems

Some gems have the property of emitting light after heating, exposure to light, or an electrical discharge. This property is known as phosphorescence, since the glow, although it is often of different colors, resembles that emitted by phosphorus.

The diamond is a mineral which exhibits this property, some of its gems after exposure to sunlight for a short time emitting a glow which can be plainly seen in a dark room. This is often stated to be a property of all diamond, but this is incorrect, some stones exhibiting no change whatever after exposure to sunlight.

Phosphorescence may also be called out in the diamond by rubbing it, especially across the fibres of a piece of wood. Among all minerals phosphorescence is best exhibited by fluorite, nearly all specimens of which will, when gently heated, emit a visible light. The color of the light varies with different varieties, and is usually not the same as the natural color of the mineral. The tints exhibited are usually greenish, bluish, or purplish.

On increased heating the phosphorescence disappears, and cannot be restored again except by passing an electric discharge through the mineral, whereupon the lost power is usually regained. The same is true of diamond. It is generally supposed that the phosphorescence of minerals results from the presence within them of particles of organic matter of the nature of hydrocarbons, which are aroused to a certain activity on heating. Of the exact nature of the phenomenon, however, little further is known.