Studying Fluorescent Rocks and Minerals with Ultraviolet Lamps

Posted by Nancy McNamara on

Here at OnlineScienceMall, we get excited about fluorescent rocks and minerals. We carry a number of handheld ultraviolet lamps suitable for collecting and studying your fluorescent minerals. They are lightweight and portable and therefore great for fieldwork. We also carry a number of mineral specimens perfect for your collection. If you have an interest in collecting, identifying and displaying fluorescent minerals, whether you’re new to the hobby or a seasoned pro, then we’ve got something exciting for you.

But first, if you’re asking yourself, “What is fluorescence?” then you’ve come to the right place, because we’re passionate about it.

What is a Fluorescent Mineral?

Some minerals have a physical property known as "fluorescence." These minerals have the ability to temporarily absorb a small amount of light and an instant later release a small amount of light of a different wavelength. This change in wavelength causes a temporary color change of the mineral in the eye of a human observer.

Fluorescence in minerals occurs when a specimen is illuminated with specific wavelengths of light, typically either ultraviolet (UV) light, x-rays or cathode rays. These types of light have the ability to excite susceptible electrons within the atomic structure of the mineral. These excited electrons temporarily jump up to a higher orbital within the mineral's atomic structure. When those electrons fall back down to their original orbital, a small amount of energy is released in the form of light. This is known as fluorescence.

The wavelength of light released from a fluorescent mineral is often distinctly different from the wavelength of the incident light. This produces a visible change in the color of the mineral. This "glow" continues as long as the mineral is illuminated with light of the proper wavelength.

Most minerals don’t have a noticeable fluorescence, and it can be an unpredictable property. Only about 15% of minerals have a fluorescence that is visible to people, and some specimens of those minerals will not fluoresce. Fluorescence usually occurs when specific impurities known as "activators" are present. These activators are typically metals such as tungsten, molybdenum, lead, boron, titanium, manganese, uranium and chromium. Fluorescence can also be caused by crystal structural defects or organic impurities. Iron and copper impurities can reduce or eliminate fluorescence.

Most minerals fluoresce a single color. Other minerals have multiple colors of fluorescence. Calcite has been known to fluoresce red, blue, white, pink, green, and orange. Some minerals are known to exhibit multiple colors of fluorescence in a single specimen. Many minerals fluoresce one color under shortwave UV light and another color under longwave UV light.

Fluorite: The Original "Fluorescent Mineral"

In 1852, George Gabriel Stokes noted the ability of fluorite to produce a blue glow when illuminated with invisible light "beyond the violet end of the spectrum." He called this phenomenon "fluorescence" after the mineral fluorite.

Many specimens of fluorite have a strong enough fluorescence that the observer can take them outside, hold them in sunlight, then move them into shade and see a color change. Only a few minerals have this level of fluorescence. Fluorite typically glows a blue-violet color under shortwave and longwave light. Some specimens are known to glow a cream or white color. Many specimens do not fluoresce. Fluorescence in fluorite is thought to be caused by the presence of yttrium, europium, samarium or organic material as activators.

Lamps for Viewing Fluorescent Minerals

The lamps used to locate and study fluorescent minerals are very different from the ultraviolet lamps (called "black lights") sold in novelty stores. The novelty lamps are not suitable for mineral studies for two reasons: 1) they emit longwave ultraviolet light (most fluorescent minerals respond to shortwave ultraviolet); and, 2) they emit a significant amount of visible light which interferes with accurate observation, but is not a problem for novelty use.

Scientific-grade lamps are produced in a variety of different wavelengths. Shortwave (SW or UVC) lamps emit light in the 100-280nm wavelength range, midwave (MW or UVB) emits in the 280-315nm range, and longwave (LW or UVA) emits in the 315-400nm range. The scientific-grade lamps used for mineral studies have a filter that allows UV wavelengths to pass but blocks most visible light that will interfere with observation. These filters are expensive and are partly responsible for the higher cost of scientific lamps.

Ultraviolet wavelengths of light are present in sunlight. They are the wavelengths that can cause sunburn. UV lamps produce the same wavelengths of light along with shortwave UV wavelengths that are blocked by the ozone layer of Earth's atmosphere.

Small UV lamps with just a few watts of power are safe for short periods of use. You should never look into the lamp, shine the lamp directly onto your skin, or shine the lamp towards the face of a person or pet. Looking into the lamp can cause serious eye injury. Shining a UV lamp onto your skin can cause "sunburn." Eye protection that blocks UV light should be worn when using any UV lamp.

Shop our Fluorescent & UV Sensitive Products and Blacklights collection. We’re also offering 20% off all our Rocks and Minerals and Geology and Rock Kits.

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