fluorescent minerals - Why do rocks glow?
Why do some minerals glow when they are illuminated with ultraviolet light?
When certain minerals are exposed to ultraviolet light, they glow brightly due to a property called “fluorescence.” Fluorescence occurs because the ultraviolet light is creating very brief changes in the smallest, subatomic parts of our mineral specimens.
Minerals are made up of different arrangements of elements (such as calcium, magnesium, fluorine, silicon, oxygen, and iron), and all elements are made up of atoms that have different numbers of protons, neutrons and electrons.
When we shine an ultraviolet light on our mineral specimens, that light “hits” the electrons in the atoms in the mineral structure and the energy of the ultraviolet light “bumps” certain electrons up to a higher energy level. But those electrons are unstable at that higher energy level, and when they fall back to their original energy level, they give off their extra energy as visible light. That visible light is the fluorescence.
Why does fluorescence have different colors?
The energy absorbed and given off when the electrons are bumped around by the ultraviolet light differs from element to element. Those differences create a variety of colors in the fluorescence of different minerals.
There are different types of ultraviolet lights. Does it make a difference?
Yes! It is critical to have the correct ultraviolet light to when working with minerals. Ultraviolet lights have different wavelengths, and minerals respond differently to the wavelength of the light. For some minerals, it is important to use a long-wave ultraviolet light with a wavelength of 365 nm. Other minerals will glow only with a short-wave ultraviolet light with wavelength of 254 nm. Some minerals won't glow at all. There are many resources available online that identify mineral responses to UV light.
Will my blacklight work for minerals?
No, or not very well! A standard black light has a wavelength of about 390 nanometers and higher. At that wavelength, the light won't have the right frequency needed to bump the electrons up to the higher energy state, and no bump means no or little glow. A standard black light used for pet urine detection or scorpion hunting at night will not work well for your minerals.
What’s the deal with filters?
An ultraviolet light used for mineral work should have a filter. The filter allows only the ultraviolet light to pass through the lens, and it prevents visible purple light from coming out of the light. That visible purple light is problematic because it can overwhelm the fluorescent glow, particularly in photographs. Take a peek at the lens of your light. If you can see the LED, it is NOT filtered and will not give you the performance you need for minerals.