FMF - Friends of Minerals Forum, discussion and message board

[nurbo]

Hi Amethystguy,
If memory serves electron valence is about having an electron or electrons in the outer shell of an atom that can be shared or even stolen by another atom, that would make a lot of sense as an explanation as to how the colour shift occurs, it seems to me it may also point to the catalyst for the reaction being heat and not light. The heat adding energy to the system causing the electron orbits to increase and that increasing the likelihood of an ionic bond being formed with another atom.
Though I might be completely wrong, its been a long time since I studied any chemistry. Im absolutely sure theres someone here who can help out with a better explanation of this than me.

[Jason]

I may be way off also but hey..can't hurt to try...It might be similar to amethyst(go figure) when in ground radiation causes the electrons to jump from +3 valence to +4 ,in turn giving it it's purple color but when left in the sun most amethyst will fade as their +4 electrons covert back to +3..this is all off the top of my head as i have read about it before and may be way off..has something to do with the UV rays? maybe?

[nurbo]

Thanks amethystguy youve given me another idea for the experiment, keeping three pieces in the dark and exposing one to LW UV one to to SW UVand the other to both to see what impact that has on the colour change properties. I have been thinking about the possibility of colour change being down to wavelengths of light, I have a Sodium light (The kind used to illuminate public buildings at night) which I may yet incorporate into this, there are a lot of permutations presenting themselves here, I hope Ive got enough Fluorite to cover them all.

[Tracy]

Hi Nurbo -

If you can use pieces from my Westmoreland fluorite that I intend to test my trimming skills on this summer, let me know and I'll gladly send some chunks with color (a lot of it is washed out, but there are still some colorful places), if I have any woth using, to help with your experiment...

- Tracy

[Peter]

I can confirm similar experience as Ryan B/ Strahler.
Most champagne colored topaz fade upon long sun exposure.
One pocket in the Kazionnitsa Pegmatite, Alabashka Pegmatite field, Urals faded after some years in non direct sunlight. Other pockets in thei pegmatite produced blue topaz.
Blue topaz from a nearby pegmatite, the famous Mokrusha vein topaz occurs as light blue, almost colorless to deep blue crystals. Some of these have a light champagne color in the core and near the termination which fades upon light exposure and seem to become light blue with time. The blue color in topaz from this pegmatite also seem to be intensified by light exposure. Topaz from Shigar, Braldu and Haramosh areas of N Pakistan of light to dark champagne to almost orange color (not the irradiated orange-brown) fade with exposure for sure and from some pegmatites rather rapidly.
Ukraininan (Volodarsk/Volhynsk) is usually a very dark orange incredible color when found in the pocket. Even small shards are brightly colored and fade rather quickly in bright sunlight. The bicolored samples found in some pockets *light pinkish champagne and blue) seem to be more stable (at least for 15 years).
Peter

[nurbo]

Hi Tracy,
That would be great, Id be happy to add some of your trimmings into the mix, my email is davidbruno(dot)uk(at)gmail(dot)com if you want to contact me whenever you've finished the somewhat nerve wracking process of trimming the specimen Ill give you my home address.
I havent been able to do the cutting and polishing of the Mexican stuff yet since I busted a sacral nerve in my back and have been pretty much unable to move for the last few days. Just as soon as Im fully mobile again Ill start a new thread (since were off topic here) with the details of what Im planning to do.
db

[nurbo]

Update ... Ive had the Fluorite in the sun for over 2 months now and no sign of any colour change when compared to a control piece I keep in an envelope in a cool cellar.