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Calcite green fluorescence activator

Posted by José Zendrera  
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José Zendrera June 04, 2012 12:44AM
Hi all,

Last night I discovered that a large calcite aggregate placed in my garden is so fluorescent. All fluo calcites in my collection turns to pink with UV but this one turns to green. Can somebody tell me how rare is this?

I have understood that the activator of pink fluorescence in calcite is manganese. Have you any idea about wich element could be the activator of green fluorescence in calcite?

Very thanks for your comments.

Parallel grow calcite aggregate with karstic origin on Miocene bioclastic conglomerate.
45 x 35 x 30 cm


Same view under LW UV LED.


Side view.


Jose
open | download - C_rom10.JPG (302.8 KB)
open | download - C_rom11.JPG (311.5 KB)
open | download - C_rom12.JPG (336.6 KB)
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Henry Barwood June 04, 2012 02:15AM
Considering the origin, I would guess the green is from organic inclusions.

Henry Barwood
Troy University
Troy, Alabama USA
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Errol Culver June 04, 2012 03:21AM
I would also consider the possibility of organic minerals as activators, however, another possibility are uranium oxides, the usual activator in green fluorescing opal and hyalite.
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José Zendrera June 04, 2012 01:28PM
Henry, Errol, very thanks for your help. After reading your post, I found some literature about organic compounds and uranium as fluorescence activators in calcite but I could not find any photo of calcite green fluorescence, I imagine is a unusual phenomenon.

This calcite is from a old Roman quarry exploted many centuries ago to built Baelo Claudia (Tarifa, Cadiz, Spain) not far from my home. I will come back there by night to chech if all calcite in the quarry is fluorescent or not.

Thanks again and greetings.

* please see my thread about fluorescence here (in spanish but with nice pictures):
http://www.foro-minerales.com/forum/viewtopic.php?t=7665

Jose
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Chester S. Lemanski, Jr. June 04, 2012 02:46PM
Jose,

My guesses were the same; however, much aragonite fluoresces this dull greenish color. Is it possible that it is aragonite intergrown with the calcite??
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Will Ruth June 04, 2012 05:50PM
^Hard to say the aragonite is entangled with the Calcite as they have the same chemical composition.
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Henry Barwood June 04, 2012 08:02PM
Look at the cleavage. Calcite has 3, aragonite only 1 (at least only 1 distinct cleavage). The two weak cleavages in aragonite are also at right angles (orthorhombic).

Henry Barwood
Troy University
Troy, Alabama USA
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Boris Erjavc June 04, 2012 09:05PM
Hi everyone,
I have fluorescent lamp, but I don`t know is it short vave or long vave UW. There is no details on it.I can only say ,that my teeth glow jellow in that light.
Thanks you all.

Boris
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José Zendrera June 05, 2012 12:30AM
Thanks for your comments and suggestions.

Even if it were aragonite, green fluorescence would be uncommon. But not, is not aragonite, as the crystals are so large, was easy to check the cleavage as pointed by Henry: always rhombohedrons with 3 cleavage planes.

Perhaps is not rare at all, I found another calcite in my collection with greenish fluorescence. The mystery remains in the activator. I imagine the proportion of activator element is so low that it will not appear in a XRD nor a EDS.

Thanks and greetings.

Calcite
Candesa Quarry, Verdenueva Height, Camargo, Cantabria, Spain.
10 x 7 x 7 cm
With halogen lamp:


With LW UV LED:


Jose
open | download - C_cam0.JPG (176.6 KB)
open | download - C_Cam7.JPG (291.7 KB)
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Rob Woodside June 05, 2012 01:01AM
Jose says:

"I imagine the proportion of activator element is so low that it will not appear in a XRD nor a EDS."

Sadly that is too often too true and is just as true for colour in visible light.
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David Sheumack June 05, 2012 11:57AM
Hello Jose,

What makes something glow? Aside from LED lights, the following is from one of my "old" chemistry textbooks, concerning phosphorescence. Generally the metal activators of phosphorescence and fluroescence are similar so maybe this is of interest. It may pose a challenge for us of today to reproduce these experiments, considering obtaining thallium salts etc. grinning smiley


From “Textbook of Inorganic Chemistry”, J.R. Partington, 5th Edit. 1939, pp 847.
Phosphorescence: “The property of shining after exposure to light, especially sunlight”

Phosphorescent calcium sulphide is obtained by heating a mixture of calcium carbonate and powdered sulphur for an hour to dull redness in a closed crucible. The mass is cooled and triturated with an alcoholic solution of various heavy metals to give 1 part of metal to 10,000 parts calcium sulphide. The mass is dried in the air and heated to dull redness for two hours and then slowly cooled.

Various phosphorescent masses are prepared by heating the mixtures A below, powdering the product, moistening with solution B, and re-heating. (All weights are in grams and volumes in cubic cm).

VIOLET LIGHT:
A: 20g calcium oxide, 6g sulphur, 2g starch, 0.5g sodium sulphate, 0.5g potassium sulphate.
B: 2cc of 0.5% bismuth nitrate solution plus 0.5 cc of aqueous thallium sulphate.
DEEP BLUE LIGHT:
A: 20g calcium oxide, 20g barium hydroxide, 6g sulphur, 1g potassium sulphate, 1g sodium sulphate, 2g lithium carbonate, 2g starch.
B: 2cc of 0.5% alcoholic bismuth nitrate plus 2 cc 0f 1% rubidium nitrate solution.
BRIGHT GREEN LIGHT:
A: 40g strontium carbonate, 6g sulphur, 1g lithium carbonate, 1g arsenic trisulphide.
B: 2cc of 0.5% thallium nitrate solution.
DEEP ORANGE RED LIGHT:
A: 40g barium carbonate, 6g sulphur, 1g lithium carbonate, 0.47g rubidium carbonate
GOLDEN YELLOW LIGHT:
A: 25g barium carbonate, 15g strontium hydroxide, 10g sulphur, 3g starch, 1g lithium sulphate, 1g magnesium oxide.
B: 2cc of 0.5% thallium sulphate plus 3cc 0f 0.4% copper sulphate solution.
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Donald Peck June 05, 2012 02:03PM
Manuel Robbins, in his book "Fluorescence", Geoscience Press, 1993, page 76, indicates that Terlingua calcites can fluoresce a pale green. He does not indicate what the activator may be; however on a later page he says that organic activators cannot be ruled out.
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José Zendrera June 05, 2012 11:56PM
Thanks David, the list seems a good recipe! Thanks Don for the reference.
Below I post another calcite from same Roman quarry, also very fluorescent.
I'm beginning to think that this material could not be rare, the quarry is full! However, I have some other stalactite samples from different places and are not fluorescent.
The quarry is the Gibralter Strait Natural Park, not far from de beach but 200 m.a.s.l. There is no road, is a 30 minutes walk from home. Next new moon I will go to check if the quarry is all fluorescent...
18 x 14 x 14 cm
With halogen lamp:


With LW UV LED:


Jose
open | download - C_15.JPG (325 KB)
open | download - C_16.JPG (323.6 KB)
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José Zendrera July 09, 2012 06:50PM
More surprises with this calcite. Yesterday I walk up to the Roman quarry where this material come from and I picked up another piece of karstic calcite. When, at night, I checked the fluorescence with a UV LED lamp, I can't belive that I see: this piece has a pink fluorescence, not green as the other pieces from same area.
There is many karstic calcite veins in this area, I imagine that different fluorescence colors must be due to different activators. One of these nights I will check the fluorescence "in situ" and I will post the results. Meanwhile, comments will be very welcome.

The quarry was used by Romans to construct Baelo-Claudia, in Tarifa, Cadiz, Spain. They prepare rough column sections at place, then they roll them to the beach (pine forest are new, this slope was a dunes erg), and transport the blocks by sea to Baelo-Claudia, 3 miles away.
The karstic calcite is in some veins as can see in the center of the wall.


Karstic calcite under halogen lamp.


Karstic calcite under UV LED lamp.


Jose
open | download - Roman quarry.JPG (251.5 KB)
open | download - calcite11.jpg (261.9 KB)
open | download - calcite12.jpg (222 KB)
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José Zendrera July 10, 2012 10:45PM
I hope not to bore you with this topic but I want to show you this. In this layered karstic calcite, some layers are fluorescent and some others are not, as can see in last pictures. Today I discovered a big piece with some layers turning to pink and some others to green under LW UV. Different layers have different activators due to different crystalizing conditions and / or different composition of water salts?

With UV LED 390 nm:


With halogen lamp:


Jose
open | download - C_karst21.jpg (250.8 KB)
open | download - C_karst22.jpg (197.4 KB)
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Rob Woodside July 10, 2012 11:23PM
Jose, if you are serious about Fluorescents you should check out http://uvminerals.org/fms/about-fluorescent-mineral-society. The FMS is currently developing a huge catalogue of Fluorescent Calcites and yours would be a good addition if not already there. They may know what your activators are. Your suggestion that traces in the depositing fluids produce the colours must be right.

Anyone seriously interested in Fluorescents should join up.
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Earl Verbeek July 11, 2012 11:07AM
Jose, your mention that this is karst-related provides some clues -- so we are apparently looking at near-surface, low-temperature calcites. Rainwater percolating through soil horizons often picks up humic and fulvic acids that form by decomposition of organic materials in the soil above cave systems. As the rainwater percolates downward through the soil horizon into the rock below, eventually to become part of the groundwater system, any calcite deposited along the way in fractures, or as stalactites, stalagmites, flowstone, etc. in the caves is apt to fluoresce because of organic activators. The organic molecules are far too large to fit into the calcite crystallographic sites, so they are present as molecular inclusions. The resultant fluorescence can cover a broad range of colors depending on which humic and fulvic acids are present and can be green, white, pink, pale blue, etc.

Here are a few guidelines:
1. Cave calcites with organic activators almost always fluoresce in some pastel (unsaturated) color: white, pink, pale green, bluish white, etc. Rich, vibrant colors would make me think of another cause. From your photographs the fluorescence seems to be pastel, consistent with organic activators.
2. Such calcite usually fluoresces more strongly LW than SW. Often the fluorescence can be activated by visible light as well, as cavers often note when sweeping their cap lamps across a cave passage and seeing a phosphorescent trail.
3. Phosphorescence is often noted in such calcites. Often the phosphorescence has a slightly "cooler" color after SW excitation than after LW. I've noted many examples where the phosphorescence after SW excitation is bluish white, but after LW excitation it is greenish white.
4. Uranium in the form of uranyl ion is another quite common cause of green fluorescence in many species (calcite, aragonite, opal, adamite...), again as molecular inclusions. However, the color of fluorescence is saturated, a vibrant yellowish green, quite unlike the pale greens caused by organic activators, and usually the fluorescence is much brighter SW than LW. Phosphorescence is usually absent.
5. Bear in mind that uranyl-activated calcite can also be found in caves (as in some of the Grand Canyon, USA occurrences), and both organic and uranyl activators of fluorescence, as well as others, can be present in the same specimen.
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José Zendrera July 12, 2012 01:28AM
Ron, following your advice, I signed up in FMS. Is a very interesting site and now I need some time to read and digest the large amount of information it contains, these days I'm busy and I still could not do it. Very thanks for your help.

Earl, thanks very much, your explanation is very helpful to understand what my eyes are seeing. I had noticed a slight phosphorescence but I thought it was psychological, from now will observe this phenomenon with more attention.
Regarding the origin of activators, the more I learn, the less I understand. At first I thought maybe you could correlate the fluorescent layer in the different veins of the quarry and see if they are contemporary, as we do in a sedimentary geological formation. But I'm not so sure I see that the cementation of the sandstone limestone containing calcite is also fluorescent at some points and they are scattered without any apparent order.

The geological history of these sandstones is short and quite thrilling. Are very young, dated as Early Pleistocene, deposited in proximal marine environment and are currently about 200 meters above sea level. Tectonic movements in the Strait of Gibraltar led to his fast climb, during which eroded most of the deposit, leaving only isolated outcrops here and there in discordant contact on older materials.
I think I will need a lot of dedication to study the fluorescence of these materials and to draw conclusions useful for the understanding of these sandstones.
I will come back again when the checks and photos of the quarry are done.
Greetings.

Wall cut from the Roman quarry. In the cave lies the fluorescent calcite:


Wall section of fluorescent calcite:


Jose
open | download - romanquarry7.jpg (374.3 KB)
open | download - romanquarry9.jpg (489.7 KB)
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Mark Willoughby July 12, 2012 12:49PM
Howdy All,

Many micro and macro sea organisms fluoresce, in various shades of green. Based on the location and age of the sandstone, plus the history given; I would suggest the fluorescence is quite likely a result of the CaCO3 being of marine origin (ie: broken down shells and exoskeletons etc.).

Given the climate will have changed little from the time of the deposition of the sandstone beds, to today, it would be fair to say that any calcite or calcrete deposits close to the surface may well have gone through numerous stages of saturation followed by drying (possibly even crystalisation).

* Calcrete (also known as caliche or kunkar) - This rock-like material forms as a soil horizon, by seasonal winter-time wetting (which dissolves the CaCO3) and summer-time drying (which precipitates the CaCO3 as a solid again). The original source of CaCO3 may have been either; part of the sandstone composition or shell grit in wind blown sand from the coast.
You will find this action is actually still happening constantly in this region today.
Extreme periods of wet can move the CaCO3 quite deep into ground if given enough time and fluid.

So being so close to the surface, even if the base deposit of calcite was hydrothermal, both it and any further additions to the deposit would almost certainly have been affected by the weather cycles and the deposition of marine based CaCO3.

The fact the sandstone has undergone periods of uplift and folding etc, I would not be at all surprised if the deposit is a mix of hydrothermal and weather based deposition. Thus; the pinkish fluorescence in some pieces, and green fluorescence in others. It is just a theory, but it may explain the results given.
I would certainly recommend the sandstone be checked under a microscope for traces of fossilised marine organisms and be tested to determine its CaCO3 content.

Just as a quick note: Calcite can also crystalise quite quickly if given the right conditions.

Hope this helps some!

Cheers Mark.

We will never have all the answers, only more questions!



Edited 1 time(s). Last edit at 07/12/2012 12:58PM by Mark Willoughby.
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José Zendrera July 12, 2012 02:26PM
Just to confirm that Mark is right assuming this sandstone has marine fossils:


This is a bioclastic sandstone containing many fossils, specially bivalve molluscs. Is locally conglomeratic (in photo), with some boulders up to 10 cm and fossils up to 5 cm:


Here karstic calcite "in situ" near to a conglomeratic zone:


I hope to post soon some pictures of the quarry by night with UV lighting.

Jose
open | download - romanquarry3.JPG (505.4 KB)
open | download - romanquarry4.JPG (483.2 KB)
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Georg Graf July 13, 2012 01:18AM
Hi Jose,

the activator in yellow or green fuorescing Calcite is very likely organic matter. (See topic "Fluorescent Calcite" in the Scrapbook of Nov. 06, 2005).

Best wishes, Georg
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José Zendrera July 13, 2012 01:47AM
Georg, in Scrapbook date of Nov. 06, 2005 I find only one message not related to fluorescence.
Perhaps date is wrong? Can you give me a link to this "Fluorescent calcite" thread?
Thanks for your help.

Jose
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Steve Stuart July 13, 2012 03:02AM
Hello, Jose!

I read with interest that the locality for your fluorescent calcite is near Tarifa, Cadiz. My wife and I will be on vacation in Spain from 16 Sept through 30 Sept and plan to be in Tarifa from 25 Sept to 26 Sept. Would it be possible to collect while I am there? Or, perhaps we can meet and trade. What might your interests be in minerals?

Kind regards,

Steve Stuart
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Georg Graf July 13, 2012 02:12PM
http://www.mindat.org/mesg-17-28031.html

Hi Jose, last post Nov. 12, 2005.

Greetings, Georg
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Bart Cannon July 13, 2012 04:34PM
As far as I know at this time, the best UV LED flashlights only radiate down to 395 nm. I believe that is longwave.

I have lost access to my Ocean Optics spectrophotometer so I can't confirm this with my UV LED flashlight.

The spectrum displayed via the OO spectrophotometer by the typical UV SW / LW high power lamps is a very complex picket fence of peaks in a continuum from "long wave to short wave".

The LED flashlights show a much cleaner spectrum, but I'm pretty sure that none of them get down to shortwave.

I hope to have my OO spectrophotometer back soon. It's worth buying one just to observe the Fraunhofer lines from the sun.

Bart



Edited 1 time(s). Last edit at 07/13/2012 04:48PM by Bart Cannon.
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Peter Haas July 13, 2012 05:33PM
A mercury vapor lamp (with peak emission at the infamous 254 nm) is an appropriate SW UV source.
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José Zendrera July 14, 2012 01:09AM
Georg, thanks for the link. I see that this is a recurrent matter. I find many related texts but few original scientific papers about fluorescence in calcite. I guess the fluorescence activators are so elusive, hard to pin down, that leave much room for uncertainty.

This calcite is much more fluorescent with LW UV than with SW UV. I checked with a small SW UV fluorescent tube lamp and there is only a very light effect. The problem with LW UV LEDs is that they emits also some visible light. Some flashlights have a filter to minimize it. I have 6 LW UV LED flashlights from 3 distinct manufacturers and there is a difference between them. Even 2 lamps of same model and same manufacturer but buyed with 1 year lapse have different emision. These differences, that can be noticed naked eye, are more evident with my small OPL spectrometer, as suggested by Bart.

Steve, you will be welcome, I will send you a PM.

I've planed walk up to the roman quarry tomorrow night, there is no moon and the weather looks good. I will carry 2 large LW UV LED flashlights, tripod, camera... hope to post some nice pictures next days.

Jose
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José Zendrera July 15, 2012 06:12PM
From many years I know these sandstones and associated calcite, it is common to find these materials on the beaches of the area. As well many years ago I "discovered" (not been mapped on the geologic map of the area) the outcrop of the Roman quarry, currently without access road and lost in the vegetation. However, just a couple of months I realized that this calcite was fluorescent. It was not until last night I went up to the quarry equipped with camera, tripod and several ultraviolet LED flashlights...

Please, see a complete report here:
http://www.foro-minerales.com/forum/viewtopic.php?p=79332#79332


FOV: 2,5 m


FOV: 3 m


FOV 1,5 m


Jose
open | download - P1090807.JPG (340 KB)
open | download - P1090912.jpg (217.9 KB)
open | download - P1090913.jpg (260.8 KB)
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Georg Graf July 19, 2012 05:10PM
Hi Jose,

a maybe interesting further reference:

Toth, Veronica A.: Spatial and Temporal Variations in the Dissolved Organic Carbon Concentrations in the Vadose Karst Waters of Marengo Cave, Indiana. - Journal of Cave and Karst Studies, 60 (3): 167 - 171. 1998

Good Luck,

Georg
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claire Brimson July 19, 2012 05:33PM
Jose.

Ive attatched a photo I took whilst underground in an gold mine. Under UV light, it has greenish 'streaks' to it. In normal LED light, it was yellow/red/brown - iron sulphide

hope this helps??
open | download - 018.JPG (246.9 KB)
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José Zendrera July 19, 2012 08:22PM
Georg, that's a nice gift, is exactly that I was looking for. I was persuaded should be possible to correlate fluorescence with any aspect of climate, to profit some information from this fluorescence, not only remain in an stunning and aesthetic effect. I just have read the abstract, but it promises to be very, very interesting. Thank you very much for this link.

Claire, also your photo is very interesting. But I have a doubt: the green fluorescence, it comes from pyrite / other iron sulphide? or it comes from the karstic calcite that grows on the wall?

Karstic calcite
Baelo - Claudia Roman quarry, Tarifa, Cádiz, Spain.
FOV: 1,5 m


Jose



Edited 1 time(s). Last edit at 07/19/2012 08:26PM by Jose Zendrera.
open | download - P1090907.JPG (188.7 KB)
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José Zendrera July 30, 2012 03:18AM
Here two calcite pieces from the same outcrop picked up a few hundred meters away.
4 x 3 x 1 and 4 x 2,5 x 1 cm

Under halogen lamp:


Under LW UV LED:


Jose



Edited 1 time(s). Last edit at 07/30/2012 03:45PM by Jose Zendrera.
open | download - C_fluoX2_1.JPG (325.2 KB)
open | download - C_fluoX2_2.JPG (282.4 KB)
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José Zendrera August 07, 2012 07:35PM
Just to show some of last photos from another outcrop in this Roman quarry. Here can see thick karstic calcite sections and some pockets. Some areas have a very strong fluorescence, with an amazing color combination.

I would appreciate suggestions and comments about these fluorescences. Thanks for your interest.

Can see a complete report of this quarry here:
http://www.foro-minerales.com/forum/viewtopic.php?t=7867

This wall is a section of a big geode colapsed by karstic calcite. On top can see some smaller pockets with acute rombohedral calcite pyramids almost covered by lichens, one of them pinnace filled:
FOV: 1,2 m


Same wall, here by night with LW UV LEDs. Some crystals fluoresce pink and some others do green:
FOV: 1,5 m


Total fluorescence festival.
FOV: 2 m
Please click on the image to see it in HD:


Jose



Edited 1 time(s). Last edit at 08/18/2012 02:01AM by Jose Zendrera.
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Rock Currier August 07, 2012 07:39PM
What is pinnace. Pinnace is usually defined as a small boat. Pinnace (ship's boat), a small vessel used as a tender to larger vessels amongst other things

Rock Currier
Crystals not pistols.
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José Zendrera August 07, 2012 10:08PM
In Spanish we call "pinaza" to pine needles that fall to the ground. As I didn't knew this word in english, I used Google translator, I see is not very reliable...


This is the pocket filled with "pinaza":


Jose
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Rock Currier August 08, 2012 09:23AM
Ah! pine needles. That makes perfect sense. I have kicked up pine needles near Crystal Peak in Teller Co., Colorado and found good quartz crystals, or at least one good smoky quartz crystal.

Rock Currier
Crystals not pistols.
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José Zendrera August 10, 2012 01:20PM
Here a psychedelic painting by Miquel Barceló ...sorry, I mean another view of this outcrop:

Karstic calcite "in situ" under LW UV
Baelo Claudia - San Bartolomé Roman quarry, Tarifa, Cádiz, Andalusia, Spain
FOV: 1,8 m


Jose
open | download - P1100079_2.JPG (504.9 KB)
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Rob Woodside August 10, 2012 06:25PM
Thanks Josele, These are really wild!
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Yan Beaudet August 12, 2012 09:36AM
hi , just a question . why we dont have our own fluorescent minerals forum here on mindat. this subject seem to interest a lot of members. The big bad ebay have create their own auctions categorie for the fluorescent minerals cause they seen than many buyer are only interested by fluorescent minerals.the numbers of members participating or just readings this topic seem to prove than a great interest exist for this kind of minerals
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José Zendrera August 12, 2012 10:51PM
Rob, thanks for your comment, I like you enjoy as I do.

Yanick, that's a good idea, you can suggest it in General section of messageboard, probably many more people will support this iniciative.

Karstic calcite "in situ" under LW UV
Baelo Claudia - San Bartolomé Roman quarry, Tarifa, Cádiz, Andalusia, Spain
FOV: 2,5 m


FOV: 1 m


Jose



Edited 1 time(s). Last edit at 08/12/2012 11:25PM by Jose Zendrera.
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open | download - P1100081.JPG (483.2 KB)
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José Zendrera September 18, 2012 10:51PM
After many visits to this amazing quarry http://www.foro-minerales.com/forum/viewtopic.php?t=7867, I can say there is two different types of fluorescence under LW UV:

1 - A pink (under LW UV LEDs) / orange (under M-LW UV "black light" tube) fluorescence. This occurs always on surface or very close to surface.

2 - A yellow- green fluorescence, wich continues to the interior of the mineral body. This fluorescence changes to first type in surface. In fact, yellow-green flurescence can be observed only in recent fractures. Is not a question of layers, when the exterior surface is perpendicular to growing layers, the pink/orange zone is also perpendicular to growing layers.

A chemist friend who accompanied me the other night to the quarry thinks that could be due to alteration by sunlight of any organic activator.

Information or comments about this possibility will be very welcome. Thanks.

Karstic calcite
Baelo-Claudia San Bartolomé quarry, Tarifa, Cádiz, Andalusia, Spain
22 x 20 x 10 cm


Same piece under LW UV LEDs. Right side was in the surface of the outcrop, left side was interior.


Another piece from the same outcrop, under M-LW UV "black light" 20W tube, with less blue visible light than LEDs. That you see pink with LEDs, here under "black light" tube is orange.
There is a exterior orange layer and a yellow-green interior, wich is more orange in the outer zone.


Jose



Edited 1 time(s). Last edit at 09/20/2012 01:36AM by Jose Zendrera.
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claire Brimson September 26, 2012 09:36PM
Jose Zendrera Wrote:
-------------------------------------------------------
> >
> Claire, also your photo is very interesting. But I
> have a doubt: the green fluorescence, it comes
> from pyrite / other iron sulphide? or it comes
> from the karstic calcite that grows on the wall?
>
>>

Hi Jose,

Apologies for not getting back to you sooner. I have been back down the mine this was taken in and the greenish colour is from calcite mixed with iron sulphide.

Claire
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