Peridot is a distinctive green gemstone, valued for its vibrant color that ranges from yellowish-green to deep olive. This gem, a variety of the mineral olivine, has been admired for centuries. Ultraviolet (UV) light represents a form of electromagnetic radiation existing beyond the violet end of the visible light spectrum. Gemologists and enthusiasts often use UV light to observe how various minerals and gemstones react to this specific energy.
Peridot’s Response to UV Light
Peridot generally exhibits a weak to inert reaction when exposed to ultraviolet light. Some specimens might display a very subtle yellowish-green fluorescence, but this effect is faint. The intensity of any observed glow is usually quite low, making it difficult to discern without optimal viewing conditions. Often, peridot appears entirely inert, showing no visible change.
A strong, vibrant glow under UV light is uncommon for peridot. Such a reaction can indicate the stone is not peridot, but rather another mineral or a synthetic material.
The Science of Peridot’s Glow
The phenomenon of fluorescence occurs when a material absorbs higher-energy invisible UV light and then re-emits it as lower-energy visible light. Electrons within the gemstone’s atomic structure absorb the UV energy, moving to a higher energy state, and then return to their original state by releasing this energy as visible light. This process is distinct from phosphorescence, where the emission of light continues even after the UV source is removed; peridot does not typically exhibit phosphorescence.
Peridot’s green color is primarily attributed to ferrous iron (Fe2+) within its crystal lattice. While some trace elements can activate fluorescence in other minerals, iron often acts as a “quencher.” This means the iron content, which gives peridot its characteristic color, absorbs energy that would otherwise be re-emitted as visible light, suppressing any fluorescent glow.
Practical UV Observation for Peridot
To observe how peridot reacts to UV light, a dark environment is recommended to enhance visibility of any subtle changes. Gemologists use specialized UV lamps that emit light at specific wavelengths, commonly longwave (LW) UV at around 365 nanometers and shortwave (SW) UV at approximately 254 nanometers. Portable lamps often combine both longwave and shortwave capabilities, allowing for comprehensive testing.
When examining peridot, look for a weak, subdued yellowish-green response, or no reaction. Eye protection, such as UV-blocking goggles, is advisable when working with UV lamps.