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Fakes & FraudsReal Russian Hackmanite?

9th Aug 2013 09:42 UTCJess Forster

I purchased a Russian hackmanite sphere a few weeks ago. It's just arrived and I am beginning to doubt it's authenticity.

I am unfamiliar with the Russian material. All Hackmanite specimens I have previously come across were from Greenland. I know that Sodalite is very fluorescent from Greenland will fluoresce bright orange under long wave UV and Hackmanite is tenebrescence. However, upon inspection of my new piece it did not fluoresce under long wave nor did it display any signs of tenebrescening.

Does the Russian variety of this mineral not fluoresce? Does it not display tenebrescence?

Does anyone else have any information on Russian Hackmanite?

Is this piece I've acquired the real deal or is it an imitation or fake?

9th Aug 2013 14:04 UTCOwen Lewis

My understanding is that strong UV LW fluorescence and tenebrescence are diagnostic for Hackmanite. However, depending on the place of origin, the tenebrescent effect can be reversed. My specimens are from Afghanistan and these tend to whiten if kept in the dark and change to a more or less deep purple in strong sunlight.

Your sphere does not look like any hackmanite I have seen. What tests have you done other then the above? SG? RI?

9th Aug 2013 15:53 UTCStephanie Martin

Hi Jess,

As Owen mentioned, try placing the sphere in direct sunlight and see if the colour changes, not sure how long this should take but should be noticeable within a few minutes if reactive. I noticed this also with my hackmanite from Burma, it is more reactive to sunlight and not so much to my low end LW light.

regards,

Stephanie :-)

10th Aug 2013 06:16 UTCJess Forster

Thank you for your help. I haven't done any other tests on it other than checking the fluorescence and tenebrescence. I've tried putting it in sunlight like you said but still no colour change. I think they got me. :(

It says in the items description on Ebay that it is from Kola Peninsula, Russia. It weighs 91 grams and is 4.3 cm but according to my measurements it's actually 39 cm. Could any of this information be helpful?

Many thanks,

Jess

10th Aug 2013 13:09 UTCOwen Lewis

Hmmmm..... your measurements give your sphere a density of about 5 gm/cm^3. That's over twice as dense as Hackmanite. If your measurements are good, then what you have cannot be hackmanite. How reliable are your instruments?

11th Aug 2013 08:17 UTCJess Forster

Hi Owen,

Thank you very much for your insight. My scales are very reliable but I did round the weight of the sphere. It's actual measurement is 90.8 grams. I have no 100% accurate way of measuring the diameter. It looked to either 38mm or 39mm when I lined it up on my ruler. The seller said it was 43mm in diameter.

Do you have any clue as to what it is I actually have here?

Thanks so much for you help!

11th Aug 2013 13:50 UTCBen Grguric Expert

If the diameter of the sphere is 3.8cm, then its radius is 1.9cm. Volume is 28.73cc. If the mass is 90.8 gms then the density is 3.16 gm/cc. Looks like more than one mineral phase. Perhaps quartz and barite.

11th Aug 2013 22:10 UTCOwen Lewis

Ben.

Thank you :-(

12th Aug 2013 02:45 UTCDoug Daniels

To further muddy things, if it is 3.9 cm in diameter, the density is 2.92 g/cc. If it is 4.3 cm, the density is 2.18 g/cc, a bit "light" for most minerals.

12th Aug 2013 14:26 UTCOwen Lewis

Would someone please buy us a calculator: :-) And Jess a pair of vernier callipers:)-D

12th Aug 2013 17:54 UTCDoug Daniels

Yes, a pair of verniers would be most helpful, assuming the piece is close to a true sphere.

12th Aug 2013 18:19 UTCStephanie Martin

Hi Jess,

You will need to test this with a shortwave lamp as you have not done that. You could probably borrow one if you belong to club or at least take it to someone who has one to check it out. Failing that try your local university. I checked out your listing, the seller is reputable and I have dealt with them many times in person. They would not be trying to dupe you although anyone can make an error. May I also suggest that you are covered under Ebay buyer protection and you can get a refund if the item is not as advertised if you send it back. You only have 45 days to do so, but I think you have time to sort this out. I would send an email to the seller through ebay and express your concerns and request that a refund be processed if you cannot determine it to be authentic Russian hackmanite.

regards,

Stephanie :-)

15th Aug 2013 12:37 UTCAmanda Hawkins

Just by sight alone it looks like a jasper to me

15th Aug 2013 17:57 UTCReiner Mielke Expert

"Hackmanite" is a variety of sodalite that is white. By that definition most "Hackmanite" is not tenebrescent but all hackmanite fluoresces under LW UV. If your sample does not fluoresce under LW UV then it is not "hackmanite". If you define hackmanite as tenebrescent sodalite then again you do not have hackmanite because all tenebrescent hackmanite also fluoresces strongly ( orange or some shade of that) under LW UV.

15th Aug 2013 19:13 UTCAlfredo Petrov Manager

Measuring the true diameter is very easy: get a cloth tape measure, wind it around the sphere and determine the circumference. Then divide by π.

15th Aug 2013 20:30 UTCDavid Baldwin

Another easy way to measure it accurately is to trap it between 2 flat surfaces, say blocks of wood, and measure the gap. It's very difficult to just 'eye' it up against a ruler.

18th Aug 2013 00:59 UTCJess Forster

Thanks for everyone's input. I do not own a short wave UV but I thought it fluoresced strongly under long wave as Reiner Mielke said.

Stephanie, I have contacted the seller now and he responded to me saying;

"I am sorry about the measurement mistake, I have a flat ruler I use and I can be off by a few mm especially with the eggs and the spheres when I measure them. As for the stone, I can assure you 100% that it is Hackmanite, my father spent 3 summers in Kola Peninsula in the 70s mining minerals for Institutes and private collections of USSR, and he spent several weeks on this deposit of the Hackmanites. A few years back he got a lot of his personal rough for polishing into cabochons, eggs and spheres, and this is one of those pieces.

I am aware that Hackmanite should fluoresce, but I just checked 2 pieces in my collection (Russian and Afghani) that the latter has a much richer color than the Russian material."

Gosh, I really do need to get vernier callipers! Good suggestion about the cloth measuring tape. I've tried it and the sphere measures 13.6 cm making its diameter 4.329 cm.

Hope this new info helps!!

18th Aug 2013 12:42 UTCOwen Lewis

Jess,

Read the reviews and buy here. http://www.amazon.co.uk/BargainUniverse%C2%AE-Digital-Micrometer---Bargain-Universe--/dp/B0071LLOCO/ref=sr_1_3?s=diy&ie=UTF8&qid=1376822929&sr=1-3&keywords=digital+vernier+calipers

At that price, there is simply no excuse not to have a pair. You can pay a lot more but will receive nothing better for your purposes.

Specimens either test out or they don't. If they don't, they are best rejected. According to http://www.mindat.org/min-1789.html , Kola is the type locality from which the properties of hackmanite were first described. Therefore, it should be assumed that 'Russian Hackmanite' (from Kola impllied by the dealer) should show the characteristic properties. AIUI, the chemical difference between sodalite and hackmanite is the presence of sulphur in the latter (this in turn accounting for the photochromatic properties). That's another way of saying that tenebrescence is diagnostic for hackmanite. As your specimen does not show this property, I'd send it back for a refund. As the specimen also shows no fluorescence, there must be a question mark over whether it is even sodalite.

Looking at the pics, I'd guess you have a rock of some sort and that all bets are off. The calculated density of 2.19 g/cm^3 for your sphere is within the typical range for sodalite and hackmanite but if your specimen is a rock the density calculation is not meaningful.

18th Aug 2013 19:08 UTCStephanie Martin

Hi Jess,

The information provided by the seller is correct as far as his father's history is concerned.

I suggested to try SW just to see if there was any reaction at all. As was noted previously my Burma hackmanite does not respond much to LW and I also have hackmanite from Bancroft, Ontario that does not respond much either. Since the Burma material responds to sunlight, it may be that it is only reactive in certain wavelengths and your LW may not be in the right range, not all UW lights are equal. That being said, I would still ask for a refund since it does not exhibit the properties you would expect from hackmanite. Interestingly, the seller also has a listing for a Russian hackmanite slab that looks very similar, which clearly shows photos of the fluorescence. The sphere listing did not have this. I would ask what type of lamp they used for the slab photo, as they do not indicate which type. The problem with asking for a refund is that I am not sure if you will receive your shipping fees back and given the weight and size you will need to determine if it is worth it to return.

regards,

stephanie :-)

18th Aug 2013 21:51 UTCOwen Lewis

Fluorescence is indicative (only) of sodalite. It can't differentiate sodalite from hackmanite (nor can RI or SG etc.). Only tenebrescence does that.

Anyone know of a different diagnostic test for hackmanite?

18th Aug 2013 22:45 UTCStephanie Martin

Owen, I want to agree with you about the tenebrescence, but what happens if the hackmanite becomes less reactive? I have read somewhere, sorry I don't remember where, that the tenebrescent effect may decrease over time if repeatedly activated. Therefore would it still be hackmanite if it eventually becomes non-reactive? Would it just be considered sodalite after the fact then?

regards,

stephanie :-)

19th Aug 2013 01:12 UTCReiner Mielke Expert

According to this paper tenebrescence has nothing to do with sulphur http://rruff.info/doclib/am/vol39/AM39_615.pdf . To use the term hackmanite for only tenebrescent sodalite is awkward since white non-tenebrescent sodalite is often intimately mixed with tenebrescent sodalite at the Davis Quarry in Bancroft. Often the tenebrescence areas occur as small spots and streaks evenly distributed throughout non-tenebrescent sodalite, other than the tenebrescence they look identical. Both the tenebrescent and non-tenebrescent sodalite fluoresce strongly in LWUV but the tenebrescent areas more so. Both fluoresce weakly in SWUV but only the tenebrescent portions become purple ( also happens in sunlight).

19th Aug 2013 01:19 UTCOwen Lewis

Stephanie,

Nassau (The Physics and Chemistry of Color) describes tenebrescence and hackmanite as follows. Hackmanite is sodalite in which part of the Cl has been replaced by S. Tenebrescence is a colour centre effect where the precursor is S2-- which produces an S2- colour centre , losing an electron. The S2- colour centre absorbs at 400nm and the free electron is trapped in a halogen vacancy forming an F centre that absorbs at 528nm, the combination of the two causing a magenta-ish colour.

The formation of the hole centres can be triggered fairly quickly by exposite to UV or slowly by IR. Hackmanite that has whitened can be slowly restored to magenta if placed in a light-proof box and warmed over time as well as being exposted to UV. The chemistry has been synthesised and is the basis of auto-adapting sunglasses that darken when exposed to sunlight that is UV-rich, fading rapidly when the ambient lighting is UV-poor.

There is nothing in this explanation which admits the reaction to 'tire' over time. However, having whitened, the hackmanite will require exposure to UV-rich light to change colour again (or IR for a long period when not exposed to any light).

Nassau does not say (but it is easy to reason) that the strength of the tenebrescence weakens as the %age of partial substitution of Cl by S reduces below some unspecified level. If anyone has information on the max, min and optimal Cl:S ratios for observable tenebrescence, that would be useful to know.

In my view, to be interesting to a collector, a specimen needs to demonstrate tenebrescence within some hoiurs of exposure to temperate region direct sunlight. Out of interest, I have just take out an looked a couple of pieces of hackmanite rough that have not seen any UV in over 6 months. Both were dirty white in room light and shows poor fluorescence under LW UV. With a few minutes exposure to LW UV the fluorescence has restored to its 'hot coals' typical appearance and the tenebrescent colour change was marked.

Best,

Owen

19th Aug 2013 01:31 UTCOwen Lewis

That's an interesting paper, Reiner but it is 60 years old.

Nassau's book (2nd edn copyright 2001) is generally accepted at the standard primer (grad level) on the causes of colour.

19th Aug 2013 02:49 UTCRob Woodside 🌟 Manager

Hackmanite was first found in Greenland by Giesecke around 1807 who called it pink sodalite. It lost its pink after fracturing, becoming a light green and was tenebrescent. In 1901 Borgstrom analysed a pink sodalite from Kola and found it contained a little sulfur, so he named it Hackmanite.

With the arrival of x-ray crystallography early in the 20th century, the idea of naming species by what were the major elements that dominated lattice positions supplanted the 19th century idea that any new chemical constituent should generate a new species. This reduced the number of species names to less than 2000 from over 4,000 and Hackmanite became a chemical variety of sodalite that contained a little sulfur.

Without the IMA protection, Hackmanite came to mean different things. The fluorescent community reserve Hackmanite for tenebrescent sodalite. Surprisingly thermal neutrons don't create tenebrescence and the structural change can be observed with high intensity neutron diffraction. The structure expands slightly on activation and relaxes somewhat on bleaching. Armstrong and Weller (2006)* argue that adjacent cages contain S₂^-2 and a vacancy. The excitation knocks an electron off the S₂^-2 and inserts it into the vacancy making a colour centre that gives the pink.

As a kid in Montreal without a UV source we called any white or light coloured sodalite Hackmanite, in distinction to "real" sodalite that was blue. Now perhaps with the availability of UV sources that definition has been expanded to what Reiner said, that it must also have yellow orange fluorescence. The blue sodalites are usually dead under UV. Here the broad yellow orange hump is the unresolved vibrational spectrum of S₂^-. However there are white sodalites that do not fluoresce.

Often very little impurities are needed to influence color or luminescence and there are over a half dozen forms of sulfur, from sulfide to sulfate, that have been found replacing Cl in the sodalite cages. In synthetic sulfosodalite all the Cl is replaced by sulfide, but this has not been found naturally. Sometimes the IMA allows names for theoretical minerals that have not been found but which are chemically obvious substitutions in real minerals, whether or not they have been synthesized. In spite of this synthesis, Hackmanite has escaped species status.

There are two other "sodalites", Nosean and Hauyne. Here sulfate is dominant in the cages, ideally replacing all the Cl. To balance the charge of the minerals ( Cl^- -> SO₄^-2), half the cages in nosean contain neutral water and in hauyne one of the Na⁺ in the cage is replaced by Ca⁺².

What about Lazurite? Well it is a sulfide rich Hauyne!!! Although the name dates from 1890, it has not suffered the fate of Hackmanite. It is still regarded as a real species, in spite of the fact that all analysed Lazurites are sulfate dominant with minor sulfide!!! I guess it is just one of those theoretical minerals.

* ARMSTRONG, A.J., Weller, M.T. (2006) Structural Observation of Photochromism. Royal Society of Chemistry, Chemical Communications, 1094-1096.

19th Aug 2013 04:46 UTCOwen Lewis

Oh dear, what do we put our hands in :-D

Rob Woodside Wrote:

-------------------------------------------------------

> .....Hackmanite became a chemical variety of sodalite

> that contained a little sulfur.

>

> Without the IMA protection, Hackmanite came to

> mean different things. The fluorescent community

> reserve Hackmanite for tenebrescent sodalite.

> Amusingly the current understanding of this

> tenebrescence is that the exciting radiation

> knocks a Cl out of the sodalite cage and it is

> replaced by an electron. The pink color is then

> the result of this colour centre. This has nothing

> to do with S!!!

Well Rob, we seem close enough. According to Nassau, one effect of the radiation is to change the S2-- to S2-, that forming a hole centre and losing an electron, this electron then being trapped in a Cl vacancy to form an F centre. These *two* colour centres work together to produce the colour as already described.This is unusual; where there is more than one centre in a crystal, typically only one is responsible for colouration

It's interesting that you quote the colour of hackmanite as pink. I have never seen it in that colour, those I have seen always being much darker, ranging from the magenta that Nassau gives to almost a purple. I suppose that a very weak magenta might be describes as pink. This could be a colour range effect as seen in corundum, where a 1-4% Cr++ substitution for Al++ produces a strong red (as a ligand field effect) but, as the Cr substitution for Al drops below 1%, the red weakens to pink, weakening further to colourless as the level of Cr present becomes insignificant.

A PhD in physical chemistry - those were the days :-), Nassau was a leading authority - perhaps the leading authority - on the causes of colour. An author of seven books on colour and crystals, he also wrote the entry for colour in the Encyclopaedia Brittanica in 1988 (still in use). A research scientist working for 30 years on crystal chemistry and physics in the AT&T labs, he was also for some years a Visiting Professor to Princeton University . He died in 2010.

19th Aug 2013 13:28 UTCBen Grguric Expert

Hate to say it Jess, but if I paid $65 for a sphere that was supposed to be sodalite var. hackmanite and it didn't show the classic tenebrescence I would be a bit hacked off. After all I presume you bid on it because you wanted a specimen that showed that unusual behaviour?? It's possible that a large lump of hackmanite-bearing material was made into a group of spheres and your particular sphere didn't contain any. Either way you didn't really get what you paid for in my opinion. The dealer should have checked it with a simple UV test at least.

19th Aug 2013 17:24 UTCReiner Mielke Expert

Hello Owen,

"Both were dirty white in room light and shows poor fluorescence under LW UV. With a few minutes exposure to LW UV the fluorescence has restored to its 'hot coals' typical appearance and the tenebrescent colour change was marked. "

That is very interesting as the Medved paper specifically says LWUV is needed for the color change. However the Hackmanite from Bancroft does not become tenebrescent under LWUV only under short wave UV and when it is tenebrescent it's response to LWUV does not change. How does your material respond to SWUV?

19th Aug 2013 18:17 UTCOwen Lewis

Reiner,

Fluorescent reaction to SW UV is weak. To test for tenebresence at SW UV will now take some weeks/months, since I must wait for the specimens to regress to their unexcited colourless (white) state.

But one can think. Tenebrescence has all to do with energy levels and those vary proportionately to the wavelength of the radiation; the shorter the wavelength the higher the energy carried by the photon. According to Nassau (I have not tried this but I think I should in due course) prolonged exposure to IR (wavelength unspecified) will cause white Hackmanite to show colour - but only if it is not exposed simultaneously to light, the average energy level of which serving to remove colour from hackmanite. Being more energetic than IR the whitening effect of light will swamp the colouring effect of IR. But UV is more energetic than light and therefore if exposed to sunlight (a mix of IR. light and UV radiation) a white hackmanite will change to show colour.

It seems to follow that either LW or SW UV should produce the tenebrescent colour change.

Best,

Owen

19th Aug 2013 19:22 UTCRob Woodside 🌟 Manager

Owen, you caught me!!! While I was writing the last post off the top of my head and saying that the pink/purple had nothing to do with sulfur, you were writing about Nassau. I didn't see that until I posted that nonsense. So I quickly read some literature rather than glancing at it and edited out the nonsense and replaced it with:

".Without the IMA protection, Hackmanite came to mean different things. The fluorescent community reserve Hackmanite for tenebrescent sodalite. Surprisingly thermal neutrons don't create tenebrescence and the structural change can be observed with high intensity neutron diffraction. The structure expands slightly on activation and relaxes somewhat on bleaching. Armstrong and Weller (2006)* argue that adjacent cages contain S₂^-2 and a vacancy. The excitation knocks an electron off the S₂^-2 and inserts it into the vacancy making a colour centre that gives the pink."

This I think is what Nassau said, but I must get a copy of his book. The comment about infra red light inducing photochromism is interesting and agrees with the oft stated claim that Hackmanite will darken in the dark.

At first I couldn't believe this because in the dark the only excitation is the energy of thermal motion due to the temperature. Currently I'm cooking 3 Hackmanites (Ladjuar Medan, Dungannon Twp., Greenland) at room temperature in the dark and will report when I have some results. The trick is to light bleach with a tungsten lamp (Owen that could speed your relaxation time) before putting them in the dark. The equilibrium colour of photochromic sodalite depends on the concentration of S₂^-2 and a nearby vacancy as well as the relative amount of UV in the illumination which darkens and the yellow in the illumination which bleaches it. This gives colours from blood red to pink to dark purple.

Stephanie, elsewhere John Duck (http://www.mindat.org/forum.php?read,106,181082,181300#msg-181300) and Reiner Mielke (private communication) have observed the Bancroft specimens decrease their photo chromism with time and activation. A couple of years ago I was visiting Marcus Origlieri in August in Tucson. When I mentioned this effect Marcus said he had picked up an Afghan piece last Tucson show and it was in the garden. It had been there in full Tucson sun for several months and when we retrieved it, it was still light purplish but it had lost its photochromism. So yes it will not cycle indefinitely.

Jess, your sphere certainly looks like Kola hackmanite, but also lots of other things. I would believe the label. It is a light coloured sodalite, most likely with a bit of sulfur. However from this thread you can see there is some disagreement over just what hackmanite is. If your definition of hackmanite requires fluorescence or photochromism, then your piece while being sodalite is according to this definition not hackmanite. This the trouble with varieties on which the IMA is silent and giving no universal definition.

19th Aug 2013 19:43 UTCDoug Daniels

I know..I shouldn't oughta do this, but......

A tentative explanation of the lack of tenebrescence in the sphere has to do with the tenth decimal inthe measurement of the sphere. This is related to the tenth chakra of the vortex drain of energy into the tenth dimension. Also influenced by changes in the PAC-10, especially if it is in the U.S. Note that this is twice that of the Fifth Dimension, so Jupiter can no longer be aligned with Mars. So, by tenaciously teasing information from the quantum mechanics (Schroedingers cat experiment), one can extrapolate that the specimen may or may not be hackmanite.

(sorry all....employer gave us few hours this week....)

19th Aug 2013 19:47 UTCRonald J. Pellar Expert

Back in the late 60's or early 70's, I was collecting at Mont St-Hilaire. While digging in a hole, I was pulling out rocks that were pink in color and placing at the edge of my hole for later packing. Low and behold, when it came time to pack them up, I could not tell them from the other rocks, as they were all the common gray with no residual pink! This was pretty characteristic of the hackmanite, that I was familiar with from there. They came out pink (not purple) and bleached very quickly.

I subsequently purchased a Mont St-Hilaire hackmanite crystal from one of the Canadian dealers that showed the more dramatic color change from white to deep purple in patchy spots.

19th Aug 2013 19:57 UTCReiner Mielke Expert

Hello Ronald,

There don't seem to be any hard rules with this stuff as the hackmanite from Davis Quarry in Bancroft turns purple in bright sunlight and bleaches in the dark. Which is odd since when you dig it up ( after 100 years in the dark) it is purple. It also bleaches in halogen and incandescent light but not completely, that requires it be kept in the dark. Might be interesting to see what happens if you freeze it? Must be some sort of chemical difference between the St.Hilaire stuff and the Bancroft stuff. On the other hand if it was a cloudy day that time in St.Hilaire maybe there wasn't enough UV getting through to counteract the effects of the other wavelengths?

19th Aug 2013 23:07 UTCRob Woodside 🌟 Manager

Doug you should publish that;-) Oops I guess you did:-D

Earlier I said:

"Stephanie, elsewhere John Duck (http://www.mindat.org/forum.php?read,106,181082,181300#msg-181300) and Reiner Mielke (private communication) have observed the Bancroft specimens decrease their photochromism with time and activation."

Again I was wrong. Reiner PM'd me to say he hadn't seen that. We have been talking about this for sometime and I'm sorry I misquoted him.

When synthetic sodalites are heat bleached white at high temperature, they sometimes recover their blue colour and a rosy hue when they cool. The big yellow orange spectral hump in fluorescing sodalite resolves into "Stagasaurus" humps and finally into separate spectral peaks as the temperature is lowered. Darkening in the dark requires thermal activation.So yes I would expect some interesting temperature effects.

Ron, I had the same experience at St Hilaire around the same time, but I never kept any as I was an element and sulfide collector then. I could not remember if all the pink I recovered was fractured off the quarry face or if I dug up the pink without fracturing. For along time I thought the energy in the propagating fracture activated the pink. However Reiner, I hope I have this right, has dug up pink out of the dirt with no fracturing.

20th Aug 2013 01:52 UTCReiner Mielke Expert

Hello Rob,

Yes you have that right. That is how we find it without a UV lamp, it comes out of the ground pink-purple without any banging on it.

20th Aug 2013 03:59 UTCDoug Daniels

Yeh, Rob, I published too soon, had some other gems to add......

I have a small piece from the obvious location of Bancroft, Ontario that I use when I talk to kids. It is about 2 cm by 2 cm; overall it fluoresces the orange/peach/whatever in LWUV. I can "charge"it with SWUV, turning some parts magenta, which will then fade (within minutes, depending on light source/intensity). I can then repeat the process. I haven't kept the specimen in complete darkness (I've had it for at least 30 yrs now); it's been in the the basement, which is fairly cool (temp-wise, that is). This discussion makes me think I might lose one of my "magic rocks". That would be a bummer.

20th Aug 2013 20:00 UTCRonald J. Pellar Expert

Reiner,

I seem to remember a cloudy day.

Rob,

We dug it up from the quarry floor. What I remember was my friend was red color blind and he kept asking me if each chunk he pulled out was pink! At the time to pack up, I might as well have been color blind too, since there was no more pink.

21st Aug 2013 06:00 UTCJess Forster

I placed the sphere on my window sill and half of the sphere was covered. The half that was exposed to the light became a slightly darker greyish-blue colour and there was a clear ling separating the two colours. Could this be the tenebresence effect I've been looking for?

21st Aug 2013 14:29 UTCReiner Mielke Expert

Hello Jess,

The short answer is no. Also I would not expect light filtered through glass to stimulate the color change since the UV would be filtered by the glass. However the effect you noticed is curious and as far as I know never been observed before. Try that same experiment in direct sunlight, if there is any tenebrescence you should notice a difference in a just a few minutes.

21st Aug 2013 15:06 UTCRob Woodside 🌟 Manager

I would respectfully disagree with Reiner. The glass will stop the short wave UV but not the long wave. The tenebrescence or photochromism is quite variable in intensity often quite blotchy with areas that darken strongly and those that appear unaffected, But it is possible to be uniform over a few cm. Try it again in full sunlight with no intervening glass and cover part of it as you previously did.

21st Aug 2013 15:10 UTCOwen Lewis

Or use a LW/SW UV light box.

16th Nov 2013 00:07 UTCBjorn S

Get a green laser to bleach the Hackmanite faster. It makes testing the tenebrescent Hackmanite faster.

P.S. My Hackmanite is from the far East and it is fluorescent under all types of UV light but won't change color under 400nm UV light. Very strong tenebrescent reaction with 365nm UV light or shorter wavelength.

16th Nov 2013 00:41 UTCReiner Mielke Expert

Looks like hackmanite from different localities changes color due to different things. This is obviously more complicated than one might think. Best of luck trying to figure it out Rob, looking forward to the results of your experiments.

16th Nov 2013 19:33 UTCRob Woodside 🌟 Manager

Reiner's right. I now think I've seen both Hackmanite and Tugtupite darkening in the dark after severe bleaching and should have some results in the new year.

29th Nov 2013 17:46 UTCReiner Mielke Expert

Rob,

Have you seen this study on Hackmanite? http://rruff.info/doclib/cm/vol21/CM21_549.pdf not sure what good it is in understanding this, maybe you can make some meaningful sense out of it?

29th Nov 2013 18:29 UTCRob Woodside 🌟 Manager

Thanks Reiner. That's a good paper. It gives a review up to 1980 and shows the ordering of the Si , Al tetrahedra. The cage contents giving the chromatic properties is a little better known now.

I'm a little puzzled by the SO₄in the probed formula and mention of SO₃ in the text: "Analyses of several grains show that sulfur

content ranges from 0.05 to 0.30 wt.% SO₃. I wonder how he sorted the two???

6th Jan 2014 19:18 UTCReiner Mielke Expert

Here is another interesting papers I came across on Hackmanite: http://rruff.info/doclib/am/vol21/AM21_764.pdf and http://rruff.info/doclib/am/vol26/AM26_437.pdf

2nd Mar 2014 14:50 UTCMark Cole

Hi - very interested in your testing of tugtupite and hackmanite tenebrescing (darkening) after being kept in the dark for some time. Any results yet?

I've read this thread and noted several comments about Canadian hackmanite tenebrescing in the dark. I have collected hundreds of sodalite/hackmanite specimens from Greenland and tested this phenomena specifically. Greenland sodalite is deeply tenebrescent upon exposure to SW UV (lightly tenebrescent after exposure to LW). It can be faded completely in seconds by direct, close exposure to UV free halogen light. Placing it in the dark for 6 months will not result in any color change.

Interestingly, almost any rock found in the field in Greenland (with some sodalite in it - which is most of them), when cracked open with a hammer, will show a deep purple color (much deeper than pink). This color fades in seconds after exposure to sunlight (bleaching). The fact that a rock does this does not mean it is tenebrescent; the color change may not occur again upon exposure to SW UV.

I have written some of this up here: http://www.minershop.com/html/all_about_tenebrescence.html

The picture attached shows a boulder of green sodalite immediately after being broken. The purple color is already starting to fade to the green color seen. This sodalite has not been exposed to any UV - but is very tenebrescent and will change color quickly upon exposure to SW UV.

5th Mar 2014 03:29 UTCPavel Kartashov Manager

Hi Jess,

don't you think, that one simple photograph of your ball give more information than all conversation on fingers?

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