- Fluorescent Minerals - USGS
Minerals come in a variety of chemical compositions, which leads to a rainbow of colors in the mineral world. Light is a form of energy, and the colors of these minerals can be considered a representation of energy in the visible portion of the light spectrum. However, there are many other portions of the spectrum that the human eye can not detect. When this form of energy, or light, shines on these minerals, the energy that is reflected is a variety of fluorescent colors, making the mineral appear as if it is glowing in the dark.
The Fluorescent Minerals
Not all minerals fluoresce, but there are a few that are very common and can be found easily in a rock shop or even out in nature. However, even these minerals may contain a slight variation in their chemical composition that will cause it not to fluoresce. But, in general, these minerals are known to be fluorescent:
- Calcite - in the visible light portion of the spectrum, calcite appears to be clear, white or light pink. Under longwave and shortwave UV light, calcite will look red, orange, green and blue.
- Benitoite - in visible light, benitoite looks blue, yellow or colorless. Under longwave and shortwave UV light, it appears blueish purple.
- Flourite - in visible light, flourite is extremely variable in its colors. It can be white, purple, green, yellow, brown, etc. Under longwave and shortwave UV light, it most commonly turns the color blue, but rarely can be white, red, purple, or green.
- Sodalite - in visible light, sodalite can be blue, white, gray and sometimes green. Under longwave and shortwave UV light, it turns purple.
- Gypsum - in visible light, it can be white, gray or colorless. Under longwave and shortwave light, it can appear white, yellow or blue.
- Quartz - quartz is most commonly clear, pink or gray in visible light. Under longwave and shortwave UV light it appears green.
Why Are Minerals Fluorescent?
Whether or not a mineral fluoresces can be traced directly to its chemical compostion. Visible light is a form of energy that is detectable by the human eye, and the colors that minerals show under visible light are a reflection of that energy. When longwave UV light (looks like a blueish purple light to the human eye) or shortwave UV light (invisible to the human eye) shines on these minerals, the electrons in the atoms of these chemicals absorb this energy and reflect it back in a form that the human eye can detect. These are the glowing, fluorescent colors that are seen under UV lights.
The visible portion of the spectrum - the portion of the spectrum that is detected by the human eye - ranges from the color red at the longest wavelength to the color purple at the shortest wavelength. The portion of the spectrum right outside the red wavelenght is the Thermal Infrared (TIR) portion. The human eye cannot detect the IR portion, but it can see where the TIR wavelengths blend into the visible red wavelengths. For example, when a stove burner gets really hot, eventually the TIR energy becomes the color red.
The same works at the other end of the visible portion of the spectrum. The ultraviolet portion of the spectrum blends into the shortest wavelength of visible light, which is the color blue. Longwave UV lights are right next to the color blue on the spectrum, so longwave UV lights, or blacklights, appear to be bluish purple to the human eye. Shortwave UV lights are not visible to the human eye (care should be taken not to look into the bulb of a shortwave UV light when it is on, as it can cause blindness even though the eye cannot detect light). So, minerals fluoresce when the electrons of the chemicals are excited by UV energy and reflect it back in forms that are visible to the human eye.
Source:
" The Fluorescent Minerals ", galleries.com
Alexandra Matiella Novak - With a PhD in Geology and expertise in science education, Alexandra is passionate about increasing the public's Earth science literacy.
