Mineral Guide > Gems > Fluorescence of Gems

Fluorescence of Gems

Closely allied to phosphorescence is fluorescence, which, in a strict sense, is the emission of light within a substance while it is being exposed to light, or in some cases to an electrical discharge from a vacuum tube.

Fluorite is again the mineral which best exhibits this property, a beam of white light passing through a colorless cube of it producing a delicate violet color. The diamond, ruby, and other gems are stated by Dana to give forth a brilliant fluorescence when exposed to an electrical discharge from the negative pole of a vacuum tube. Fluorescence is also produced in the diamond by radio-active substances; that is, by radium, or substances possessing its activity. In this respect diamond differs from such gem minerals as ruby, emerald, topaz, etc., and from glass, in none of which do the radium rays excite much activity.

The behavior of gems toward X-rays or Rontgen rays varies with different species, and affords a means of distinguishing them. Thus diamond is quite transparent to the rays, while glass is opaque.

The behavior of others of the gem minerals in relation to the X-rays is further shown in the following table:

COMPLETELY TRANSPARENT
Amber
Jet
Diamond

STRONGLY TRANSPARENT
Corundum

TRANSPARENT
Opal
Andalusite
Cyanite
Chrysoberyl

SEMI-TRANSPARENT
Quartz
Labradorite
Adular
Topaz

SLIGHTLY TRANSPARENT
Spinel
Essonite (Garnet)
Fluorite

ALMOST OPAQUE
Gypsum
Turquois
Tourmaline
Calcite

OPAQUE
Almandite (Garnet)
Beryl
Epidote
Rutile
Hematite
Pyrite
Zircon