Fluorescent Minerals: Rocks that get excited... under ultraviolet light!

Geoscience Australia

Fluorescence in minerals occurs when a specific wavelength of light such as ultraviolet (UV) light, electron beams or x-rays are directed at it. This light excites electrons in the mineral causing them to temporarily jump to a higher orbit in the atomic structure. Once the electron returns to its previous orbit, a small amount of energy is released in the form of a different wavelength of light than what's being shone onto it. This produces a visible colour change of the mineral that we see and is the phenomenon known as fluorescence.

Only about 10% of minerals have a fluorescence that is visible to humans, these minerals must contain 'activators' (cations of metal) in specific concentrations. Different metal activators will produce different colours.

Willemite, franklinite and calcite under normal light. This specimen hails from Sterling Hill near Franklin, New Jersey, U.S.A. Dubbed the 'Fluorescent Mineral Capital of the World' Franklin is home to approximately 60 different fluorescing minerals.

The next slide shows Willemite (green), franklinite and calcite (red-orange) under UV light. Only the franklinite does not fluoresce.

Langbanite forms in crystalline limestones and manganese rich skarns in metamorphosed manganese deposits. It is named after the type locality Långban, Sweden.

Named in 1821 in honour of Carl Wilhelm Scheele, Scheelite is a primary tungsten ore mineral that displays a distinct blue fluorescence. Miners and geologists would often use this to their advantage in the search by using a UV light at night time to locate the tungsten.

Calcite has been known to fluoresce many colours including red as shown above, blue, white, pink, green and orange.

Apophyllite crystal under UV light.

Did you know that some rocks can have as many as 5 or 6 minerals fluoresce on a single specimen. These represent several stages of growth from parent solutions with changing compositions and are highly prized by collectors.

Pictured are some of the UV lamp equipment used during the photography work. The large lamp has a selectable split-tube 254nm shortwave and 365nm long wave light source as some minerals fluoresce at different wavelengths. Whilst the UV pen was used to focus the light onto specific areas of particular minerals, such as the apophyllite specimen shown earlier.

Credits: Story

The National Mineral and Commonwealth Paleontological Collection, Geoscience Australia and The National Museum of Australia Mineral Collections (specimens).

Some specimens loaned from the Peter Butler Collection.

Chris Fitzgerald (photography).

Steven Petkovski (text).

Dave Champion (scientific review).

Copyright for content: http://www.ga.gov.au/copyright

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.
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