Many minerals fluoresce in a dark environment when exposed to UV light. The excitation of the atomic structure causes energy to be absorbed, some used and the excess energy given off as visible light. This phenomenon occurs directly within the willemite structure or through an activator impurity in the structure such as manganese in red fluorescent calcite. All willemites tend to fluoresce. Fluorite from Weardale fluoresces brightly purple while fluorite from Derbyshire rarely fluoresces.

Calcite, Rio Grande del Sol, Brazil.

UV fluorescent collectors use two wavelengths short wave (SW) at around 254 nm wavelength and long wave (LW) around 365 nm. SW is the UV that reddens your skin in sunshine while LW will give you a brown tan. Care should be taken to sensibly minimise your exposure to UV light and it is advisable to use plastic goggles, particularly with SW.

Willemite, Franklin, N.J.

Some minerals fluoresce different colors in LW and SW. A good example is calcite from Halecombe quarry, Somerset. It fluoresces bright blue in SW, pink in LW and has long blue phosphorescence. Phosphorescence is when the mineral continues to glow after the UV light has been switched off.

Calcite, Halecombe Quarry, Somerset (SW).

Calcite, Halecombe Quarry, Somerset (LW).

Collectors focus on obtaining specimens with the maximum brightness, several colours from differing minerals, vein structures, special colours or for phosphorescence. Fluorescent minerals can be found in many places in the UK including, for example, the Mendips, Weardale & Leicestershire. Worldwide the range is enormous with Franklin N.J., Langban Sweden, Mt. St. Hilaire among the collectors' favourites for their variety.

Calcite, Halecombe. Phosph. after 3 secs.

Sphalerite (SW), Sterling Hill Mine, Franklin, N.J.

Tirodite in tremolite, Balmat, N.Y.

Clinohedrite, hardystonite, willemite & calcite, Franklin, N.J.

Agrellite, Kipawa, Quebec.

Several UK members of the Russell Society are keen fluorescent collectors and are also members of the worldwide group the Fluorescent Mineral Society and a number of UK specimens donated by them are on display at the Warren Museum of Fluorescence at Sterling Hill Mine, New Jersey, including Mendip calcites and Weardale fluorites. A visit to these websites will give you links to many sources of information on mineral fluorescence.

Willemite phosphorescence, Sterling Hill Mine, Franklin, N.J.

For further details, comments or queries about fluorescent minerals please contact Gavin Malcolm directly on

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