Fluorescent Minerals & Types Of Luminescence
What Are Luminescence, Fluorescence, Phosphorescence, & Tenebrescence?
Luminescence: A collective term for the emission of visible light under the influence of certain rays (other than incandescent and daylight), as well as by some physical or chemical reaction, but not including pure heat radiation. It is most commonly seen as fluorescence under ultraviolet lighting.
Fluorescence: An instantaneous optical effect arising from the movement of electrons within the structure of a material. It is most commonly observed by exposure to shortwave and/or longwave ultraviolet lamps. Or, the emission of visible light by a substance exposed to ultraviolet light.
Phosphorescence: This may occur after fluorescence. The energy from some shifting electrons (caused by exposure to shortwave and/or longwave ultraviolet lamps) can be "stored" within the material and be released at a later time. If the energy release is delayed for a period of seconds, minutes, hours, or days, it is known as phosphorescence. Or, a mineral which continues to glow for an interval after the ultraviolet light source has been turned off.
Tenebrescence: It is also known as reversible photochromism. It is the ability of certain minerals to change color when exposed to sunlight and other types of illumination, such as ultraviolet lighting. The effects can be repeated indefinitely, but will be destroyed by heating. It is most commonly seen in the minerals Tugtupite and the Hackmanite variety of Sodalite.
What Is Really Going On?
Ultraviolet (UV)light is electromagnetic radiation in a part of the spectrum between X-rays and visible light, approximately 180 nanometers to 400 nanometers. It differs from light only that its wavelengths are too short to be seen by the human eye. Longwave UV-A radiation is 315-400 nanometers. Midwave UV-B radiation, is 280 nanometers to 315 nanometers. Shortwave UV-C radiation, is 200-280 nanometers and below.
The phenomenon known as fluorescence occurs at the subatomic level by a process called electron excitation. Electrons are subatomic particles that orbit the nucleus of an atom at specific distances known as electron shells. These shells are arranged in layers around the nucleus, the exact number of electrons and their shells depending on the type of atom (element). The electrons contained in the shells nearest the nucleus carry less energy than the electrons in the outer shells.
When certain atoms are exposed to ultraviolet (UV) light, a photon (particle of light energy) of UV will cause an electron residing in a lower-energy inner electron shell to be temporarily boosted to a higher-energy outer shell. When this occurs the electron is said to be "excited." It will then drop back to its original inner electron shell, releasing its extra energy in the form of a photon of visible light. This visible light is the fluorescent color that our eyes perceive. The exact color depends on the wavelength of the visible light emitted, with the wavelength itself being dependent on the type of atom undergoing the electron excitation.
The specific atoms which undergo the fluorescence are known as activators. They are usually present as impurities in the normal molecular structure of the mineral, but sometimes are an intrinsic part of the mineral's composition. In fluorescent minerals, very often the activators are cations, which are atoms or molecules which carry a net positive charge (due to the loss of one or more electrons, each of which display a negative charge). For example, the activator which causes the bright red fluorescence of calcite is the Manganese cation. A cation which has lost two electrons is also referred to as divalent; three electrons, trivalent; four, quadrivalent, etc. Activators can also sometimes be anions (containing a net negative charge). The most commonly known activators of fluorescence are: Tungstate and Molybdate Ions, Uranyl Ions, Mercury, Lead, Boron, Titanium, Manganese, Chromium, Disulfide Ions, and the Rare Earth Elements. **For further information about the Rare Earth Elements, click here: Rare Earth Elements
In some cases a mineral specimen will continue to emit visible light for a period of less than a second to several minutes or more after the UV light source is taken away, with the luminosity gradually fading away. This is known as phosphorescence, and occurs because the excited electrons are slow in returning to their original electron shells.
Fluorescent minerals will usually respond best to either shortwave UV light or long-wave UV light. Some minerals may fluoresce under both wavelengths with the same or a similar color, while some may show different colors under each. Most respond best to only one of the two. However, not every mineral of the same variety acts the same under UV light. For example, not all Calcite or all Fluorite specimens will fluoresce the same, or at all under UV light. It all depends on their entire composition.
There are also minerals which will quench (not activate) fluorescence. Most commonly known as "quenchers" are Iron, Copper, Nickel, and Cobalt. The quenchers may also be referred to as “poisoners” or suppressors. Some minerals containing minute abounts of these elements may still fluoresce. Fluorescence may also be referred to as luminesence.
***Eye protection must be used when working with shortwave , midwave, and longwave UV light sources, even if for only short periods of time. Damage to the eyes will occur. Damage to the eyes which can occur are photokeratitis (inflammation of the cornea), conjunctivitis, inflammation of the conjunctiva, and retinal lesions. The first two may be referred to as "welder's flash" and "snow blindness." Do NOT look into any UV light source without eye protection!***
Which Minerals Fluoresce?
**The minerals listed below, or some of their varieties, are most frequently known to be fluorescent under shortwave and/or longwave UV light. Don’t forget that there will always be exceptions. Some minerals which you will expect to fluoresce will not, while some you do not expect to fluoresce may. Personally, I inspect every mineral (and a few other things) entering my door with my UV lights, and I have received many pleasant surprises over the years!
Adamite, Agate, Albite, Alexandrite, Allophane, Alunite, Amazonite, Amber, Amblygonite, Amethyst, Ammonite, Analcime, Andalusite, Andersonite, Anglesite, Anhydrite, Anthophyllite, Apatite, Aphthitalite, Apophyllite, Aragonite, Autunite, Aventurine, Axinite, Baratovite, Barite, Barylite, Becquerelite, Benitoite, Benstonite, Boltwoodite, Boracite, Brucite, Cahnite, Calcite, Calomel, Carpathite/Karpatite, Celestite, Cerussite, Chalcedony, Chiastolite, Chondrodite, Chrysoberyl, Clinohedrite, Colemanite, Coral, Cowlesite, Creedite, Curtisite, Dakeite, Danburite, Datolite, Deweylite, Diamond, Diopside, Dolomite, Dumortierite, Dypingite, Emerald, Esperite, Ettringite, Euclase, Eucryptite, Fluorite, Foshagite, Fossils, Gaylussite, Gowerite, Guerinite, Gypsum/Selenite, Hackmanite, Halite, Hambergite, Hanksite, Hardystonite, Hedyphane, Hemimorphite, Herderite, Hiddenite, Hodgkinsonite, Howlite, Hyalite, Hydroboracite, Hydrozincite, Ivory, Jadeite, Kornerupine, Kunzite, Kyanite, Labradorite, Lapis Lazuli, Laumontite, Leucite, Magnesite, Manganapatite, Margarite, Margarosanite, Melanophlogite, Mesolite, Meta-autunite, Metauranopilite, Meyerhofferite, Microcline, Montebrasite, Moonstone, Moss Agate, Morganite, Nahcolite, Natrolite, Nepheline, Norbergite, Novacekite, Opal, Pearls, Pectolite, Periclase, Petalite, Phenakite, Phlogopite, Phosgenite, Phosphophyllite, Phosphuranylite, Picropharmacolite, Pirssonite, Plombierite, Pollucite, Powellite, Prehnite, Pyrophyllite, Quartz, Rhodochrosite, Rose Quartz, Rosenhahnite, Ruby, Sapphire, Scapolite, Scheelite, Schroekingerite, Serpentine, Simpsonite, Smithsonite, Smoky Quartz, Sodalite, Soddyite, Sphalerite, Spinel, Stilbite, Stolzite, Strontianite, Svabite, Swartzite, Taaffeite, Talc, Terlinguaite, Thaumasite, Thomsonite, Thorite, Tincalconite, Tirodite, Titanite/Sphene, Topaz, Tourmaline, Tremolite, Trona, Tugtupite, Turneaureite, Turquoise, Tyuyamunite, Ulexite, Uralolite, Uranocircite, Uranopilite, Variscite, Walstromite, Wavellite, Wernerite, Whewellite, Wickenburgite, Willemite, Witherite, Wollastonite, Wulfenite, Wurtzite, Xonotlite, Zektzerite, Zippeite, Zincite (rarely), and Zircon.
**And many more!
What Are Thermoluminescence & Triboluminescence?
Thermoluminescence: A phenomenon exhibited in certain minerals in which they give off light, like a glow, when heated. This can only be observed in a dark area. Some minerals which exhibit this property are: Apatite, Calcite, Fluorite, Lepidolite, and some Feldspars.
Triboluminescence: A property exhibited by certain minerals which causes them to give off orange or yellow flashes of light when they are sawed or struck together. It is best observed in a dark area. Some minerals which exhibit this property are: Amblygonite, Calcite, Fluorite, Lepidolite, Pectolite, and Sphalerite.
A Willemite, Calcite, & Franklinite Orb From Franklin, NJ Shown Under Shortwave UV Light (L) & In Daylight (R)
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