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GeneralColor Change in Fluorite

15th Sep 2011 22:04 UTCRick Dalrymple Expert

I recently came across a large pile of pink fluorite on a mine dump (Cross Bow Mine, Dugway Mountains, Tooele Co. Utah). When I first came across the pile it was pale rose quartz color. As I picked up the pieces I realized they were pale green on the bottom. Nearly every piece was like this.

I am sure these pieces have been on this dump for years if not decades in direct sunlight. I am now wondering if anyone knows of fluorite that changes color due to light. They have been inside now for a couple of weeks and the color seems stable.

More speculation: this fluorite seems very dense. I thought it may be baryte it is so heavy but it is to hard (4 and baryte wont scratch it) and it is fluorescent blue/white in parts. Is a combination of barite/fluorite possible?

There is no reaction to HCl.

Any thoughts are appreciated.

16th Sep 2011 00:42 UTCReiner Mielke Expert

Fluorite commonly changes color in sunlight eventually fading to colorless. Even dark purple fluorite will become colorless with time in the sun.

16th Sep 2011 00:58 UTCRick Dalrymple Expert

Reiner,

Thanks, I know fluorite will fade but does it tend to fade to another color? This fluorite appears to have "faded" from green to pink.

16th Sep 2011 01:34 UTCScott Sadlocha

Rick,

Could it possibly have been color zoned fluorite that was green and purple, with the purple fading to pink? How is the color distributed in the crystals?

16th Sep 2011 02:22 UTCRick Dalrymple Expert

Scott,

There aren't any distinct crystals. It is massive. Here is the picture I uploaded of the mine dump.

Maybe I am barking up the wrong tree but it appears that the pink is on top and the green is on the bottom. I am going to head back out there in the next month or so. I will take the gear to go underground. I didn't have it with me when I found this so I didn't venture more than a hundred feet in or so.

The color change is fairly consistent from the pink to the green in all the pieces I have cut so far.

16th Sep 2011 13:03 UTCReiner Mielke Expert

The pink may be due to included hematite that only becomes noticeable when the green fades.

16th Sep 2011 15:43 UTCRick Dalrymple Expert

Reiner,

That would make since. There is plenty of hematite in and on the fluorite.

16th Sep 2011 15:48 UTCColin Robinson

A lot of green fluorite from Weardale will fade to pale purple if left in sunlight. Sometimes this can be a very pinkish purple and sometimes the colour can disappear altogether. I've seen some fluorites change colour in seconds as soon as the crystals are exposed. It is a very common phenomenon.

16th Sep 2011 16:40 UTCRick Dalrymple Expert

Colin,

Thanks for that information. I wasn't aware that Weardale fluorite was so light sensitive.

16th Sep 2011 19:32 UTCDean Allum Expert

Rick,

Try this experiment to confirm what Reiner has said: use a blowtorch to heat a small piece of bicolor fluorite to red hot. When it cools down, it will probably be uniformly light pink.

-Dean Allum

17th Sep 2011 00:28 UTCNik Nikiforou

Rick,

According to one of the major importers of the "pink" Fluorite fom Mina Navidad in Durango, Mexico, it comes out of the ground a dark green color and must be left out in the sun to turn pink.

Nik

17th Sep 2011 10:57 UTCRoger Curry

Hi Rick,

As Colin has pointed out, some of the fluorite from here in the north of England can be a quite attractive green - paler and less intense than Heights or Rogerley - when you first expose a new vug to the light of day. I'm off to the Hudeshope mines in Teesdale later today, I've recently found rapid fading green fluorite there. It changes to a dissapointing grey in minutes. If I get any, I'll wrap it in aluminium foil and try and video the fading in direct sunlight (should we get any, its very dull outside at the moment... in fact its hoying down). I would be very interested to find out what is actually happening, the effect can be quite dramatic. Has anyone got before and after pics of light activated colour change fluorite?

I've noticed that crystals I've put on the dashboard, when I'm back at the camper van, fade slower than those in sunlight that has not passed through the windscreen glass. So it's the UV that's doing it. Perhaps you could could try an experiment Rick. Chop out a lump of the green fluorite and expose it to the the light from an arc welder for a few minutes. The broadband UV should hit it with months of equivalent sunlight exposure.

Regards,

Rog.

17th Sep 2011 11:07 UTCPeter Lyckberg Expert

Yes, certainly some fluorite do change color with light exposure.

A giant fluorite pod in skarn (with some small molybdenite as a ring a few cm from its edge) had very strong purple color (some even reddish) at the 220 m level of the Yxsjöberg mine and changed color upon sun exposure with time.

This fluorite was exceptionally easy to give some energy immediately taken up by valence electrons (and yes some heat and sound....) and then gradually lost in the form of a yellowish-green visible light emitted, if beating on it with the sledge hammer.

(or shone at by the head light, or heated....)

The color changed during the years to a light sky blue to finally become white and specimens then looking close to quartz.

Yes fluorite is a fairly dense mineral.

18th Sep 2011 04:52 UTCHoward Heitner

The topaz-margarite-sulfide bearing veins exposed at Trumbull, Connecticut in the late 1990's were filled with blood red massive fluorite that rapidly faded to colorless in sunlight. The fluorite faded more slowly in artificial light. The only way to preserve the red color was to immediately wrap the specimen in several layers of newspaper and put it in a box.

18th Sep 2011 22:06 UTCColin Robinson

I'm off to the Hudeshope mines in Teesdale later today

Please be aware that these mines are on land belonging to the Raby Estate and they DO NOT allow mineral collecting. The gamekeepers have a habit of watching what you're up to with high power binoculars and have been known to call the police if they think you are acting a bit suspicious. It is also the grouse season and they get a bit twitchy about people wandering about.

19th Sep 2011 05:19 UTCRoger Curry

Thanks for that info Colin, I didn't know that. I'll ensure I only take photos in that area. I didn't find any green fluorite anyway!

Cheers & regards,

Rog

19th Sep 2011 16:33 UTCJesse Fisher Expert

Green fluorite from the various Weardale localities (Rogerley, Heights, Cement Quarry) is unstable and will fade over time if left in direct sunlight. Rogerley fluorite will generally do so slowly, though I have seen specimens from the Cement Quarry that will fade in a matter of hours. The resulting color is usually a pale purple due to layers of purple within the fluorite. Weardale purples seem quite stable, and I have collected bits of purple fluorite from mine tips at the middle level of the Greenlaws mine that have likely been exposed to the sun for many years.

19th Sep 2011 18:43 UTCStephen Moreton Expert

I can confirm Jesse's observations that Weardale green gradually turns purple on prolonged exposure to sunlight. Does anyone know how it can be reversed? Purple and amber seem to be stable judging by the number of times I've seen those colours exposed on mine tips.

Colin is also right about the estate in Teesdale. It is not for nothing that they've been informally renamed "Rabies estate" by some collectors I know. They have long been awkward. Although it doesn't mean you can collect, much of the high ground is access land, so if you stick by the rules you can, at least, walk across it (which must wind them up terribly, ha ha), although it would certainly be prudent to stick to Sundays (no shooting) during the shooting season. Look at the noticeboards at the footpath access points. They will say when it is "open" for walkers. There's at least one such at the head of Hudeshope.

19th Sep 2011 22:04 UTCRick Dalrymple Expert

Reiner & Dean,

I heated up 3 pieces that exhibited both pink and green. It was a little tricky as it kept blasting off small red-hot shards that burned wholes in my shirt and arms.

The pink in all three turned to green until they cooled off. After they cooled off they were white with only a little color remaining on the bottom side. This is contrary to the expected results of the experiment.

Thoughts?

19th Sep 2011 22:04 UTCRick Dalrymple Expert

I did a before and after photo but I don't have the cord for my phone here. I will have to upload them tonight when I get home.

21st Sep 2011 00:38 UTCRick Dalrymple Expert

Ok, the photos from my phone didn't turn out usable. The above info is correct though.

23rd Sep 2011 04:44 UTCDean Allum Expert

Rick,

Your experimental results are interesting (sorry about the minor explosions). They suggest that the pink coloring is due to prolonged exposure to solar UV. I expect that you will be placing a piece in the sun green-side up.

Or perhaps the white state is now due to extensive fractures. Soaking in water or mineral spirits could determine this.

Regards,

Dean Allum

26th Sep 2011 16:55 UTCRick Dalrymple Expert

Dean,

I cut a piece and put it in the sun a week ago. I see no noticeable change as of today. I suspect the pieces I found on the dump have been there for decades and they have not changed completely. I will keep you up to date for the next decade or so>:D< In reality, I am sure I will have forgotten all about this long before then.

26th Sep 2011 20:01 UTCLeonard Piszkiewicz

Many years ago I worked for and had access to an industrial irradiation facility to do some experiments irradiating various minerals. I didn't irradiate any fluorite but did several others. The premise was that minerals with colors that fade on mine dumps in sunlight do so because displaced electrons caused by natural radioactivity migrate back to their normal positions because of UV light and thereby remove the color. For example, clear barite from Palos Verdes, California goes from colorless to typical barite blue with about 2 megarads of gamma radiation from a cobalt-60 source. Placing such an irradiated specimen in direct sunlight bleaches out the blue color within one day. In another experiment, I took an attractive but colorless specimen of creedite I found on the dump of the Anaconda/Liberty mine north of Tonopah and irradiated it to a dose af about 200 kilorads, as I recall, which I calculated was about the natural dose it would have received given the age of the deposit and the average presence of radioactive isotopes in the area (mostly potassium-40). The creedite became the attractive lilac-purple typical of the non-sunlight-exposed creedite found there. Conclusion: colored minerals that fade in sunlight do so because the colors result from natural radioactivity. Colors that don't fade are colored for other reasons.

27th Sep 2011 09:24 UTCRoger Curry

Rick,

Perhaps you have a mate who works as a welder. Get him/her to sellotape (scotch-tape) a small piece of the green stuff to their welding mask. A couple of days at work using an electric arc welder will give the specimen a good blast of UV!

The beauty of this experiment is that should any undesirable side effects occur, you yourself will be unharmed this time! Just kidding, nowt dangerous will happen....

Rog

5th Oct 2011 17:00 UTCRick Dalrymple Expert

Thanks everyone for your comments and suggestions.

22nd Jul 2013 04:56 UTCJop Geurtjens

Hello everyone, Thanks for this interesting discussion. I came across an interesting Fluorite phenomenon myself, that puzzles me a bit. I live in Missoula Montana, and have been to the famous Snowbird mine a few times, near Idaho border, well known for Parisite and Fluorite. It became one of my favorite collecting sites, but because of it's relative remoteness, and my wife's evolving pregnancy, I'm there not as often as I would like ( I've seen beautiful examples of smokey and skeleton quartz, and pyrite cubes included in quartz from this locality, something that is not to be found on Mindat!)

The issue for me is this: Normally, Fluorite from this locality is fractured and heavily included. It comes in the colors light green or dark purple, at least normally!.Two very nice crystal hunters and dealers I know, Dave and Dan, sometimes unearth remarkable pockets there. Two weeks ago, they found sky blue Fluorite crystals there, think of radiated aquamarine, maybe a bit more steely blue, of which I purchased three pieces. The pieces are fairly big,(the biggest one more than 20 centimeters wide) and have semi cubic form and clear etch figures. I was surprised, when it became night, that when viewed in 'lamp' light, the pieces appear lilac/purple. Of course I googled this ''Alexandrite'' effect, and the only reference I quickly came upon, where Fluorites found on the Wanni glacier, in the Binn valley area in Swiss, where Fluorites occur that are light green by daylight, and pink by lamp(is that Incandescent?) light. The explanation was that the abundance of rare earth elements in that area in Switserland might be responsible for that effect.

Back to snowbird mine, there are rare earths in the form of abundant Parisite crystals, and a lot of radiation, showing in various shades of Smokey quartz, often pretty fractious.. The pieces of fluorite I purchased, in fact, came from a vein in the mountain, next to the main mine adit, where they are accompanied by big smokey quartz crystals(almost all of them damaged, but with great color and good luster)

My question is twofold. If the Alexandrite effect is caused by the occurrence of rare earth-elements on this location,(because of the Parisite) does that mean that this effect will prove stable? On the other hand, with so much proof of natural radiation, should I have to fear for the overall stability of the color? If so, is keeping them out of the sun enough to safeguard their stability? And, is the color mainly influenced by the radiation, or the rare earth elements?

Sorry for this booklet people, I wanted to make the problem clear within a context. Any help is appreciated, If needed i can make and upload photo's of the pieces, cheers Jop

22nd Jul 2013 18:06 UTCDennis Tryon

If you have a question, why would you not upload the pictures???

Dennis

23rd Jul 2013 06:10 UTCJop Geurtjens

Asking a question is not the same as uploading a picture, it's also easier, that's why I gave a description. The subject doesn't need a picture to be talked about. But given the subject, I understand your curiosity, it's a mineral site after all. I will try to photograph the effect and show you. My question remains the same, how likely will my pieces be stable as for color and or Alexandrite effect? I'm not very knowledgeable about Fluorite(and digital photography for that matter...), and then I came upon this thread. I just made some evening photo's, but it turns out they are all between 2 and 3mb, as are most of my pics. This message will only accept 1000 kb files. please have patience, while i will try to figure this out, maybe change a setting? I still appreciate all info people can give me on the subject, cheers Jop

23rd Jul 2013 18:37 UTCReiner Mielke Expert

The color change you see is the result of different light sources. We have blue fluorite here that is not associated with REEs or radioactivity that looks blue in sunlight but purple in incandescent light. I would expect it to become colorless if left in the sun for a long time. However, I don't know how long that would take as I have not tried that experiment .

23rd Jul 2013 23:18 UTCBarry Miller

A question - so what happens to the value of a fluorite that loses its color? For instance, I have an approximately 5 inch specimen of fluorite (from Bingham, NM) that has lost its blue color on the side exposed to the light. (The bottom portion that is not exposed to the light has retained most of the blue color.) By what percentage would you say the value has decreased?

Edited to add: (P.S. please don't move this post to Mineral Valuation. I'm not interested in knowing the value of this specimen - it's not important to me. I'm just curious about the general decrease in value of a specimen that has lost its natural mineral color.)

24th Jul 2013 01:24 UTCReiner Mielke Expert

It is worth considerably less, I would say about 90% less.

24th Jul 2013 05:48 UTCJop Geurtjens

Thanks for the info. I'll keep my Fluorite's indoor for now! Well, I finally figured out how to change photo-size! I realise now I'm years behind int his department. I was always pretty lazy when it comes to photography. Again, quality is not great but it will show the color-change. First three depict blue daylight color. This proves difficult to photograph by the way, since even photographing them makes the color somehow duller, and less blue. The first photo shows also a more ''typical'' Fluorite from Snowbird, lightgreen, no colorchange, for contrast.

24th Jul 2013 12:45 UTCRock Currier Expert

The fading and color changes in specimens over time because of exposure to light have been known for more than 100 years, but it seem to come as a fresh surprise to each new generation of collectors.

In his Popular Guide to Minerals (1912), Louis Gratacap wrote unhappily of the deterioration of many specimens in the Clarence Bement collection at the American Museum of Natural History:

I have noticed that specimens of even vanadinite, descloizite, and rhodonite, loose something of their initial brilliancy and intensity under the scourge of that actinic bombardment to which they become exposed in our halls. The fluorites, pink quartzes, even the delicate greens of some spodumene, the faintly blushing calcites and the rhodochrosites, also sensibly succumb to these exposures, while it is a matter of common annoyance to find that the realgars, cerargyrites proustites, cuprites, crocoite, and sulphurs go through changes that slowly alter their substance, texture and appearance. Stibnite looses its splendent surface, cut topazes pale, and some colors in barite slowly vanish. Mercury minerals are altered, cerargyrite changes and andorite tarnishes.1

Those who do not know history are doomed to repeat it.

24th Jul 2013 15:42 UTCJop Geurtjens

Thanks Reiner and Rock, good to be aware of these things. I have to admit that for many years I predominantly collected more durable, or harder, minerals, partly because of fascination with gem minerals, but also because of said durability. For a time I would never pick up any specimen below, say, 5 on scale of Mohs, and try to bypass more vulnerable species. Not much Calcite or Vanadinite in my collection. Over time, interests change, and increasingly I'm allowing esthetic vulnerable pieces into the collection. Some of the processes Rock talks about, I've come across, even color change in Fluorite. I' ve nevertheless been surprised by how quick this colorless can happen, apparently. Ok, next three photo's, same pieces, one more of the big crystal by day, for good measure, and then two by night

24th Jul 2013 19:12 UTCDon Saathoff Expert

When Cookie & I were working on the big pocket of cobalt blue fluorites at the prospect near the Nakye mine in Sierra Co., NM we made the mistake of leaving some specimens uncovered in the sun outside the prospect. Fortunately we hadn't uncovered the really nice groups or floater xls yet. We actually timed the decay from cobalt blue to milky white in some pieces - one and a half hours!!! The material is VERY phototropic so what we traded off went with a warning! We donated a nice group to the Museum in Socorro which is obviously not on display.

Don S.

24th Jul 2013 22:45 UTCBarry Miller

Is it known just why fluorite fades in the sun? Has anyone ever been able to restore the color?

25th Jul 2013 01:23 UTCPhil Richardson

Rick,

I was in that mine probably 20 years ago, with my collecting partner at the time, Solon Hammack. We located a fluorite vein about 1 1/2" wide which was green on both exterior sides of the vein, about 3/16" wide each, and pale purple in the middle. It was roughly crystalline, somewhat granular, and had no discernible pockets/voids. As I recall, Solon did find some small green octahedrons in another part of the mine, and all I recovered was a small section of the vein. (Thought it was neat to see a chunk of fluorite that had a green rind and purple interior.) At the time, I assumed that the dump material was purple fluorite that had faded.

Phil

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