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Educationfluorescence and crystal damage

22nd Dec 2014 00:06 UTCDennis McCoy

I have noticed on several mineral specimens that areas where the crystals are bruised or otherwise damaged seem to fluoresce more than undamaged portions. Why is this? is it just the added reflective surfaces or is there another mechanism at work?

Here are photos of an "Oskaloosa Calcite" specimen. Note that the areas of broken crystal fluoresce several time brighter than the undamaged crystals. (Please ignore the reflected, blue, visible light.)

22nd Dec 2014 00:50 UTCReiner Mielke Expert

The unbroken crystals have a coating that does not fluoresce as much.

22nd Dec 2014 11:21 UTCEd Clopton 🌟 Expert

I have also noticed some cases where bruised areas of calcite appear to fluoresce more brightly than intact areas, even when no obvious coating is involved, as on different areas of a freshly cleaved surface. I have assumed that the difference is due to disruption of molecular bonds in the crystal structure, but my knowledge of physics extends only to suspecting that such a thing is possible and doesn't allow me to offer a definitive explanation. Can someone who knows about crystal chemistry and the physics of fluorescence enlighten us?

22nd Dec 2014 13:07 UTCJoel Dyer

Hi Dennis,

I was myself pondering on the issue of fluorescent topaz(?!) from a certain location, as topaz isn't particularly well known for fluorescence, if I'm not totally mistaken. Most topaz samples that I've come accross don't fluorescent, but then my samples have been limited to few localities, to be honest.

My fluorescent topaz specimens were not covered by any coating and did not contain any unusual, easily identifiable foreign inclusions, and the SW UV reaction was medium-strength greenish-yellow, but not all the location's crystals were fluorescent, despite similar in appearance and color. These topaz specimens were long prismatic ones, of geenish tint and only somewhat translucent in thin slivers, thus, non-gemmy and somewhat broken internally.

I spoke to an experienced geological researcher, well versed in gemstones, polarization microscopy and fluorescent minerals. This person said that he had sometimes noted fluorescence in some broken topaz crystals form other locations, but not in intact, semi-gemmy topaz specimens from the same locality. The reason for the fluorescence is unclear - and would require several very expensive equipments' labtime to try & find out possible reasons, and justifiable reasons for the expense, with unsure results...

Cheers,

22nd Dec 2014 15:23 UTCJosé Zendrera 🌟 Manager

I noticed just the opposite! I have a sodalite specimen which is partially broken and the broken surface is less fluorescent than the intact faces.

BTW, I confirm that topaz from Pakistan use to be fluorescent.

Topaz

Skardu District, Baltistan, Gilgit-Baltistan (Northern Areas), Pakistan

Dimensions: 8 x 6.5 x 5 cm

This bicolor, pleochroic topaz have a brown core and a transparent exterior zone that turns to green under short wave UV. Can see normal color clicking at the picture.

22nd Dec 2014 16:48 UTCChester S. Lemanski, Jr.

This is a phenomena that I have noticed over the years. It is also the reason why fluorescent collections may include large "clunkers" with a lot of damaged crystals. They simply fluoresce brighter! I speculated that it had something to do with the physical properties of the surface layers of crystals.

Chet Lemanski

22nd Dec 2014 17:57 UTCRob Woodside 🌟 Manager

Thanks Chet! I never realized this. More than one person has entered the fluorescent community with the idea of "educating" fluorescent collectors to collect gorgeous damage free daylight pieces that fluoresce well to no avail.

I think the variability in luminescence would be from inhomogeneity of the activator, partial coatings, and multiple reflections from damage as mentioned earlier. There's lots of energy available as a mineral fractures and some of that can alter the electronic states and alter the colour. Some sodalites will start white, break pink, and quickly fade back to white. I would think that electronic states that were altered by fracturing would relax back to give the unfractured color due to the thermal energy present.

22nd Dec 2014 18:39 UTCDennis McCoy

Jose, In the case of your sodalite specimen it could be argued that the weathered surface crystals were the damaged ones, and thus fluoresce more than the unweathered (less damaged) surface in the break.

23rd Dec 2014 00:07 UTCLawrie Berthelsen (2)

About 35 years ago, a friend and I went fossicking to the Mud Tank Zircon fields at the Harts Range in the Northern Territory of Australia. He had a portable UV light with him, and we had visions of big gem quality Zircons jumping out at us. We soon discovered to our disappointment that was not the case.

Indeed, the ground lit up under the UV like the stars in the night sky, but when we tried to pick each piece up, we found that they were the tiniest, crappiest looking pieces imaginable. Later testing showed us that the gemmier the Zircon, the less it fluoresced. Conversely, the only ones that we found that fluoresced were non-gemmy broken chips, so I expect they would have been bruised, as stated above.

Seasons greetings to all, Lawrie.

26th Dec 2014 14:45 UTCAlfred L. Ostrander

While it is true that minerals will variably fluoresce along crystallographic planes due to the variance in inclusions that cause fluorescence, I am thinking along a different line. I think that psychology comes into play in that some of us fluorescent collectors enjoy the shock factor. It is one thing to see a beautifully colored and well formed specimen. It is something else to see a really ugly lump of rock and then hit it with black light and get a very satisfying reaction. That can really get some attention. Think about it. Yes, Franklin, New Jersey has a lot of rare minerals but not a lot of finely crystallized specimens. It is no wonder Franklin bills itself as the fluorescent capitol the world. All those ugly rocks under normal light blazing in the darkness of black light, especially when the one wall is fired up to blaze in the darkness.

Secondly, who really wants some of those ugly (read worthless) banged up rocks with all those damaged crystals. Worse yet, no euhedral or subhedral anything! Collectors of fluorescent minerals hold specimens to an entirely different set of standards. How brightly does it fluoresce? How many colors does it show? And yes, how ugly is that raw chunk of nothing under regular light. Let's see how we can make it really light up! Just musing a bit here...

Best Regards,

Al O

26th Dec 2014 15:57 UTCRob Woodside 🌟 Manager

Al, I think you caught the difference between fluorescent and pretty mineral collectors!

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