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| UV Lamps Fluorescent Minerals |
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How fluorescence works. This page is not meant to be an authority on the subject; it's just a quick primer on fluorescence as it applies to minerals. There is no need to delve into the mathematics of fluorescence and photon emission here; such can be found in most physical chemistry textbooks.
1. What does "fluorescence" mean? Where did the name come from?
"Fluorescence" refers to emission of light caused when a material absorbs light (electromagnetic energy) of one wavelength and re-emits light of another. An [oversimplified] example: light of 254 nanometer wavelength (shortwave ultraviolet) is shined upon willemite; the willemite absorbs the energy of this light and re-emits the energy as visible, green light.
The name "fluorescence" actually stems from the mineral fluorite, in which
the phenomenon was first observed. Not all fluorite is fluorescent, however.
The name fluorite comes from the Latin word for "flow" (fleure); the
mineral was and still is used as a flux in steel processing.2. Who should collect fluorescent minerals?
Anyone can collect fluorescent minerals. Fluorescent minerals do not have the inherent dangers of radioactive minerals (however, there are certain fluorescent minerals which also happen to be radioactive-- see below). The primary entry cost to the hobby is the price of a good, shortwave ultraviolet lamp.
3. Are fluorescent minerals dangerous? What about UV light?
Most fluorescent minerals are NOT radioactive at all; only certain ones (such as autunite, novacekite, uranocircite, and andersonite) have radioactivity because they contain uranium and / or thorium.
The phenomenon of fluorescence does not depend on ionizing radiation or radioactivity. It just so happens that a few uranium minerals are fluorescent because of the chemical properties of the uranyl ion (UO2++). Some minerals have uranyl ion as an "activator", but it's present in such tiny amounts that they're not detectably radioactive.
The only source of "danger" in most cases (unless one accumulates a large collection of uranium minerals) is the shortwave ultraviolet lamp used to view the rocks. Short-wave UV can cause sunburn if it's shined on the skin too long or too often; too much sunburn can theoretically cause skin cancer. (also, DO NOT look directly at the shortwave lamp if you're not wearing UV-shielding goggles-- see question 3B, below).
Shortwave UV, although able to cause sunburn, is not considered "radioactivity" in the everyday sense. Its energy is not high enough to cause ionization in the manner of X-rays or gamma rays.
3A. Does UV light reflect from the rocks?
Some UV does reflect from the rocks and other surfaces. Exposure to short-wave UV can give you a temporary condition called actinoconjunctivitis. It feels like sand in the eyes and usually goes away within a day. The author of this article has had one or two episodes of actinoconjunctivitis, with no noticeable after-effects. It could have been prevented by wearing safety goggles (see below).
3B. How dangerous is short-wave UV?
How can I protect my eyes?
The immediate effect of too much short-wave UV is actinoconjunctivitis; this is temporary. Repeated, long-term exposure to UV can cause cataracts (exposure includes not only UV lamps, but also spending too much time in the sun without eye protection).
There's no reason to take the risk. It's quite easy to solve: just wear safety goggles that block UV. That settles the matter.
Most of the goggles on the market will block shortwave UV. If they are made of polycarbonate, they will block UV. If in doubt, ask the manufacturer.
Wear your goggles every time the lamp is turned on.
4. What causes fluorescence?
Every atom has one or more electrons orbiting around a nucleus. At any given time, each electron has a certain, discrete energy level. Some photons (light) can interact with an electron and make it "jump up" to a higher energy level. The electron does not stay that way for very long, however, and it soon "drops back" to its original energy level. The energy it had absorbed is now ejected as another photon. Depending on the energy of the light that was shined on it, the electron configuration of the atom, and certain other factors, the ejected photon will have a specific energy and therefore a specific wavelength. With visible light, this corresponds to the color we see. The emitted wavelength will always* be longer (have less energy) than the absorbed wavelength. UV light could not cause an object to emit X-rays, for example. (*NOTE: There are substances which do not conform to this "law". They are called "anti-Stokes" materials. Such a material might need to absorb two or three longer-wavelength photons at the same time in order to emit a single shorter-wavelength photon.)
Some minerals fluoresce because their normal, pure composition has the
aforementioned properties of being able to absorb and re-emit photons (example:
scheelite, powellite). Other minerals are fluorescent because of impurities
in their composition which give them this property (example: calcite with
impurities of manganese). Traces of dysprosium are thought to cause the orange
fluorescence of some zircon specimens, but pure zircon itself does not fluoresce.
Other minerals may have flaws in their crystal structure that can make
them fluorescent. Still others may contain elements that prevent fluorescence
from happening at all; a well-known example is iron. (Notice that iron minerals,
such as siderite, typically aren't fluorescent.)
For more detailed descriptions of how fluorescence works, there are a
number of books available on the subject, such as The Collector's Book
of Fluorescent Minerals by Manuel Robbins (1983). Some physics texts
also have discussions of fluorescence, though usually from a quantum-mechanical
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