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Sometimes fluorescent
  
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Tom Mazanec




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PostPosted: Feb 27, 2021 08:28    Post subject: Sometimes fluorescent  

Sometimes I read things like "Mazanecite is sometimes fluorescent."
"Sometimes"?
What would make one specimen of a chemical substance fluorescent when another specimen with the exact same chemical composition is not?
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Bergur_E_Sigurdarson




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PostPosted: Feb 27, 2021 08:34    Post subject: Re: Sometimes fluorescent  

Sometimes the fluorescence is not caused by the basic elements of the mineral.
Decent example is Beryl var. Emerald.
In that case iron, vanadium and chromium are the microelements that cause the colour, none of which are intrinsic to the basic Beryl, and the amounts of those three affect whether the Emerald will luminate or not. Too much iron and it wont, and more chromium means higher likelihood of red showing.
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James Catmur
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PostPosted: Feb 27, 2021 10:30    Post subject: Re: Sometimes fluorescent  

Fluorite (the source of the term) is the same. Some localities do and some do not. So a northern English one is likely to be fluorescent (depending on the mine) but a Spanish one is not.

That can help you work out what mineral it is and where it is from, but not always

James
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SteveB




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PostPosted: Feb 27, 2021 11:42    Post subject: Re: Sometimes fluorescent  

Tom Mazanec wrote:
with the exact same chemical composition


I think this is key to your question, you wont find two specimens of the same mineral that have an EXACT matching chemical composition. There are certain elements whose presence in a mineral in particular ratios are characteristic to call it mineral X instead of mineral Y. Measuring these things there is a margin of error and ratios tend to match to one or two decimal places but measuring to ten decimal places are not going to be exact.

How picky are you going to get?

The raw materials that created each mineral in the earth were not measured out to the atom in a set recipe so there are variations and too much of one thing thing or another and often a different mineral will be formed. Partly this may be a mineral in the same location. Called an associated mineral which people also look for as a possible indicator what they want is in the area.

So differences in UV reaction are at the simplest due to slight differences in the mineral itself. Plus you need to understand that in the ground or inside a cavity the atmosphere a mineral is exposed to is different to what we live in. As a result when you take some minerals out of the ground they can react with water in the air to change their chemical composition, others react to light too to similarly change and over time change their appearence subtly. For example crocoite can come out of the ground a bright vibrant red colour but over time in your collection can dull towards a browner red.

Another thing to consider is there are many wavelengths of UV light and a mineral will respond to a specific range of wavelengths to different amounts. Most people have heard of UVA, UVB and UVC being associated with health risks. These cover different ranges of wavelength, but with mineralogy and printed security features the terms LongWave and ShortWave are used; LWUV and SWUV to cover wavelength ranges and UV torches/bulbs cover these to differing degrees and amounts. The cheap typical torches you buy thatgive you a purple light are outputting blue light and some of the longwave range of UV. UV light is invisible And the energies of UV photons can be very high from the sun, enough to break some chemical bonds. Sun faded book covers in store windows is the most obvious that we can see. Because the very strong invisible shortwave wavelengths of UV light can break chemical bonds its why its important that we cover up and use sunblock when going outdoors as breaking chemical bonds in people leads to cancers. Cloudy days dont block the dangerous UV rays either, theres just no way we can look outside and see if its safe or not to go out without a shirt to do some gardening or fossicking. LW UV torches (those purple ones) will only show some fluorescence present in a mineral specimens and possibly zero is the specimen is reactive to the shortwave UV. I’ve seen postage stamps that use features reactive to LW as well as SW UV separately as security features and so you need a light strong around a specific wavelength to see one but not the other. I’ve never seen a bulb that can cover the whole UV light spectra. So if you want to use UV in your mineral hunting you need several torches really of good quality to strongly cover the possibilities.

So if you buy a specimen it will look different from the seller to you because you will be using different “UV lights” which wont be covering the same wavelengths strongly. So even if you do have two specimens of exact chemical composition and send me one and keep one yourself, the uv reaction will look different to me from you because we will be using different UV light sources.

Clearer now?
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alfredo
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PostPosted: Feb 27, 2021 16:12    Post subject: Re: Sometimes fluorescent  

James : "...but a Spanish one is not."

... unless it's from Papiol, in Catalonia, in which case it will have blindingly bright fluorescence. ;))
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Jesse Fisher




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PostPosted: Feb 28, 2021 01:15    Post subject: Re: Sometimes fluorescent  

In 1858 British chemist George Stokes defined the concept of fluorescence, based in part of his observations of the reaction of fluorite from the Weardale area of Northern England. Fluorite from this region occurs in a variety of colors, which do not show a uniform response to UV illumination. Purple and green varieties show a strong fluorescence where-as yellow and colorless much less so. This suggests that the fluorescent response is somehow related to the mechanisms that are responsible tor the different colors, which may have something to do variations in the an elevated REE concentration that is known to occur in fluorite from the area. Interesting questions awaiting someone who is obsessive enough to invest time and money in analyzing the issue further.
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