UV fluorescence simulator

When stones light up in the dark

Fluorescence is one of mineralogy's most spectacular phenomena: under an ultraviolet lamp, certain ordinary-looking minerals begin to glow in improbable colours. A dull fluorite turns intense blue-violet, a grey calcite blazes red-orange, a drab willemite explodes into neon green. Our simulator lets you switch between daylight and UV lamp for ten emblematic fluorescent stones.

How it works

The mineral absorbs ultraviolet rays — invisible to the eye — and re-emits them in the visible spectrum, at a longer wavelength. The phenomenon takes its name from fluorite, where it was first described. It is caused by impurities in minute quantities, known as “activators”: traces of manganese, lead, chromium or uranium (perfectly harmless in hyalite opal, rest assured) are enough to trigger the effect.

A real identification tool, for the price of a coffee

This is what makes the UV lamp so interesting for the amateur: it costs very little and provides a serious clue. Genuine amber fluoresces a characteristic milky blue — an excellent test against plastic or copal imitations. Natural ruby emits a vivid glowing red. About a third of diamonds react in blue. Scheelite shines such a bright blue-white that prospectors used to hunt for it at night with a UV lamp.

A crucial point often overlooked: the absence of fluorescence is information too. Quartz, amethyst and tourmaline generally do not react — so if your “amber” stays dark under UV, be suspicious. Two wavelengths exist: long-wave UV (365 nm, the most common and the safest) and short-wave UV (254 nm, more revealing but hazardous to eyes and skin: never look directly at it, and wear protective glasses).