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Techniques for CollectorsNorth Pennine Fluorites - light-sensitivity

6th Jan 2006 21:21 UTCLloyd Llewellyn Expert

Having made my new 'dark cabinet', I'm now wondering about the best way to prioritize its population.

At the moment, I'm working on the assumption that the green colours are worst affected by colour loss due to exposure to daylight, having had a bad experience with a Rogerley piece collected in the 1970's (pre-mine) and kept on the mantlepiece. There was also a light blueish green piece from Heights Quarry which has become almost colourless over the last 15 years, or wasn't it as good when I found it as I now perceive it to have been?

I also know that some of the Nenthead fluorites, which tend to be a fairly unattractive dirty yellow colour in tungsten light, exhibit a pretty, pinkish daylight fluorescence. Does this become permanent after prolonged exposure?

Many of the deepest purple material I've seen on the dumps at Greenlaws, I suspect to have been exposed to sunlight for many years. Is it my imagination, or are they a much deeper colour than fluorite freshly dug from the dump?

I, personally, cannot say that I've seen any of my purple fluorites fade in colour as significantly as that green one - am I being lulled into a false sense of security?

Any shared experience, negative or 'positive', would be much appreciated even though I think this has been discussed, somewhere, on Mindat before. (Though I'm blessed if I can find it)

8th Jan 2006 20:27 UTCJesse Fisher Expert

Hello Lloyd:

My experience with Weardale greens is that specimens from the Rogerley, Heights, Cement Quarry, and the old White's Level are all potentially unstable, though to varying degrees. We mined one zone (the Solstice Pocket) in the Rogerley in 2001 that produced some very nice deep greens. Some of these would permanently change almost instantly to a muddy gray-green if exposed to a LWUV lamp. Exposure to direct sunlight would have the same effect, but took a few days rather than seconds. Greens from other areas of the mine appear more stable, but will still fade in direct sunlight over time (a few months to a few years). The resulting color is a pale purple, which I think represents the stable purple portion of the original color.

I've seen washed out looking greens from the other Weardale mines, and assume that the same thing happens to them. I don't know about the dark greens that sometimes came out of Frazer's.

I think purples are pretty stable. I have a nice Frazers twin that's been in my display almost since I first got it about 15 years ago, and it still looks like concentrated grape jelly. The purples on the Greenlaws dump have been there for who knows how many years, and I suspect may be even more purple now, due to fading of other color components.

Yellows are pretty rare from around Weardale, so I don't have much experience with that color. My Hiltons seem pretty stable, however.

I've got a few Rogerleys on display, but unless the internal halogen lights are turned on, the ambient light is pretty dim. I haven't noticed any problems yet, but they've only been out of the ground a few years. Out of paranoia, I usually keep my best ones in drawers, however, or rotate them so none are out for too long.

Cheers,

Jesse

10th Jan 2006 12:47 UTCLloyd L

Thanks Jesse. That's really scary!

I'll use the blacklight with care.

Plenty of yellow at Greenlaws, too. Unlike Hilton and Yorkshire specimens, the Weardale and Nenthead yellows fluoresce in LWUV, so I wonder if their colour-retention is different.

See you in the summer,

Lloyd

12th Jan 2006 04:28 UTCJesse Fisher Expert

Hello Lloyd;

Both Weardale greens and purples fluoresce intensely under LWUV. As the purple color appears stable, while the green not, I would assume that the fluorescence and body color of the fluorite are caused by seperate, possibly unrelated mechanisms. If you feel like experimenting on a Weardale or Nenthead yellow, please let me know what happens. I don't have one of "sacrificial" quality, myself. First round at the Lion will be on me.

If anyone is interested in putting together a black light display of Weardale fluorites, the crummy Rogerleys fluoresce every bit as nicely as the good ones, and you'll likely be less upset if the color changes as a result.

Cheers,

Jesse

16th Jun 2008 09:07 UTCLloyd Llewellyn Expert

Having recently collected some pale green fluorite from underground in the Cowshill area, I can confirm that this changes to purple almost immediately on exposure to daylight (not even direct sunlight!). These went purple while I was unwrapping and washing them.

This phenomenon is also mentioned with regard to fluorite from the Middlehope Mine (also working veins towards Cowshill) on the University of Durham Speleological Association's website at:

http://www.dur.ac.uk/speleological.association/

Very interesting, but also somewhat frustrating if you like greens!

16th Jun 2008 11:29 UTCPhilip Mostmans Expert

Surely I can add West Pastures fluorite to that list, changing rapidly from a nice yellow green to a more greenish purple. While cleaning an old bit from the mine a small crystal accidentaly came loose and I left it in the sun for 2 hours and it displayed a permantent shift to green with purple zoning (while previously these colours were only exposed in direct daylight)

I keep all my green weardale fluos in drawers at all times. The only exception is a fluorite from Rogerley (which I think is from seven dwarfs pocket) which is on the second shelf in a display cabinet. I have a piece of deep green frazers (cubes to 8cm) displaying a phenomenal purple florescence, but I won't risk it to test its reactivity to constant sunlight.

Haven't got any problems with the Rampgill yellow so far... (should I be concerned?). I agree with Jesse, Hilton specimens looks pretty stable to me.

However I have one specimen from Riggs opencast that does exactly the opposite (changes from colourless to a vague teint of purple).

Best wishes,

Philip

3rd Sep 2008 22:48 UTCHarjo Neutkens Manager

Guys, would halogen light affect the colour of the green Fluorites?

See, I like them a lot so I have the light on in the cabinet every evening........I wouldn't want the to fade though.

4th Sep 2008 02:37 UTCJesse Fisher Expert

Hello Harjo,

I have halogen lighting in my cabinet and have not noticed any ill effects on various North Pennine fluorites. I think the potential damger with halogens and fluorite is heat buildup in the cabinet if you have too much wattage and not enough ventilation.

20th Sep 2008 21:29 UTCStephen Moreton Expert

I can confirm that Hilton yellow fluorite is stable. Apart from the fact that weathered material in the tip is still yellow after decades of exposure, I have left pieces (badly dinged rejects, of course) on a south facing patio for years and they remain yellow. Likewise for Jug vein material from Brownley Hill mine. Heights green went murky purple within months, while a rather murky greyish one actually improved, turning purple. It is now back indoors! I have some fine crystals from the Blue Circle Qy. that are a disappointing grey, so I left them out for a whole summer, and they stayed stubbornly grey, sigh. Curiously the purple from the stream at Greenlaws seems to be a lighter, more vivid shade, than much of the intense dark purple we got from inside the mine (before the hostile new landowner aggressively - and possibly illegally - forced us out), although we were starting to get lighter shades in the far reaches, including good amber/purple zoned examples. These fluoresce fiercely in sunlight, but I have not tried prolonged exposure. I was told once that irradiation can restore the green colour in formerly green specimens, but I do not know if this is true.

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