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Light Sensitive Mineral List

Posted by Peter Hargis  
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Fred E. Davis September 25, 2009 01:03AM
I use a flashlight (mini-maglite), desklamp, etc. The sun's down right now so I can't repeat a sunlight exposure. I recall trying a He-Ne laser to see if a long wavelength would fade it, but as I recall, it did not.

A 60-watt bright-white CFL effected a complete fade in about 15 seconds.

A 60-watt soft-white CFL (with more red & less blue) caused a partial fade in about 15 seconds, and a nearly complete (but not full) fade in one minute. This is consistent with the He-Ne laser test. So, it takes short wavelengths to fade, and even shorter (UV) to recharge.



Edited 2 time(s). Last edit at 09/25/2009 01:18AM by Fred E. Davis.
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Rob Woodside September 25, 2009 01:14AM
Thanks Fred. Those are Tungsten sources with not a lot of UV. At St Hilaire I found these pink rocks that blanched even in direct sunlight. I'll check my Hackmanite in Direct Sunlight now at the 49th parallel. I'll see if I can check this with my Hackmanite. I've got a laser pointer and maybe I'll spring for a second desk lamp.
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Fred E. Davis September 25, 2009 01:20AM
I think we may have crossed messages. Sorry, no more edits to the old message. If I have further info to report, it'll be in a new message. Let me know what you find! Curiosity killed the cat, but satisfaction brought him back!
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Reiner Mielke September 25, 2009 01:06PM
When I experimented with radioactivity and hackmanite I noticed no change for the first 48hrs, try exposing your sample longer and make sure it is in the dark. When I got my samples of Hackmanite home from the Davis Quarry I went to wash them in the sunshine and expected the colour to fade instead it got more intense. I then went into the house and got a sample from an earlier trip that had faded and when I held it in the sun it turned pink-purple. The only conclusion I could come to is that on high UV index days the effect of the UV overcomes the negative effect of the other wavelengths. On cloudy days or days with low UV index this does not happen. It is also possible that hackmanite from different sources behaves differently.
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Fred E. Davis September 25, 2009 04:20PM
If I can get results in 15 seconds with visible and UV light, and the effects of radioactivity take 172,800 seconds or more, then radioactivity must not be a major contributor to tenebrescence.
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Reiner Mielke September 26, 2009 01:45AM
Hello Fred,

In the short term I would agree. It has been a week now and the specimen has not noticeably darkened any more. However, on a scale of years it may have a significant effect. How else can one explain the brightly coloured tenebrescent hackmanite that one finds buried deep in the waste piles at the mine, but that turn white in the dark of one's basement. After all water doesn't noticeably dissolve limestone in 15 seconds but we all know that doesn't prove anything.
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Rob Woodside September 26, 2009 02:05AM
Minoscam has a great set of articles:
http://www.minsocam.org/MSA/AmMin/TOC/
but sadly you can't copy exerpts.

Medved in 1954 wrote about tenebrescence and hackmanite in:
Edit: http://www.minsocam.org/ammin/AM39/AM39_615.pdf
and mentioned that Robert Allen in his 1834 Manual of Mineralogy first reported it. However mineralogists being sensible people knew that was silly and ignored it for nearly 100 years. This tradition, of which I am guilty, seems to have plagued the field ever since, Medved also reported that Lee in 1901 observed both the darkening and the bleaching when exposed to light in the wavelength ranges 2280- 4800 A and 4800- 7500 A respectively. Medved goes on to say, "The peak efficieciency of bleaching occurs at wavelengths shorter than yellow. Following reversal there is some partial recovery of colouration if the specimen is kept in the dark for more than five weeks." Using simple ideas of band theory and F centres he concocts a simple model to explain these features from his observered absorption spectra.

A year later Kirk in:
http://www.minsocam.org/ammin/AM40/AM40_22.pdf
repeats the story that after fracturing Hackmanite fades quickly in daylight and "The pink colour returns when the mineral is kept in the dark for a few weeks." Kirk's real contribution was to realize that the were two absobtion bands one at 5300 A and one at around 5800 A. Medved had found the latter and the former which hid in it is really an F center and said to be responsible for sodalite's blue colour. An F centre occurs when ionizing radiation knocks a negative ion out of its lattice site and a single electron falls into that hole. So if that is the case then ambient radiation is responsible for sodalite's blue colour.Kirk also gives good information on fluorescence and heat bleaching. His primary conclusion is to finger sufur as the colouring agent!!! It gets better.

RRUFF is also an excellent source for literature. Sadly some journals are caught in the internet squeeze and won't let RRUFF post them but below the specimen descrption you can click on the "view file" and see those that do, The Canadian Mineralogist is one that does and in 1979 they published:
http://rruff.info/uploads/CM17_39.pdf

Blue Sodalite by Annersten and Hassib drops the claim about the colour returning in the dark. They give some good heating data and dispose of Medved's F theory for the 5800 absorbtion. They observe fogginess in blue sodalite, an improved conductivity for blue sodalite over heat bleached sodalite. and a free single electron spin resonance. From these data the conclusion is obvious!!! The blue colour is due to colliodal particles of metallic sodium!!! Nevermind the F centres!!! I'm surprised the referee didn't ask them to insert a warning that sodalites could prove a fire hazzard on washing with water!!! So the tradition begun by mineralogists in 1834 has been well honoured down the years and most recently by me thinking that tenebrescence was just a long lived phosphorescence. I'd be intersted in hearing about any further work done in the last thirty years.



Edited 3 time(s). Last edit at 09/26/2009 05:40PM by Rob Woodside.
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Fred E. Davis September 26, 2009 10:10AM
> How else can one explain the brightly coloured tenebrescent hackmanite that one finds buried deep in the
> waste piles at the mine, but that turn white in the dark of one's basement.

They formed with the bright color, and are bleached when exposed to white light. That seems self evident.

There's another interesting discussion in "Fluorescence: Gems and Minerals Under Ultraviolet Light" by Manuel Robbins, Geoscience Press, 1994, ISBN 0-945005-13-X. There are a variety of expressions of tenebrescence, and effects vary. Note in particular on p. 131:

"Most researchers appear to agree that F-Centers are the cause, or at least part of the cause, of reversible color in hackmanite. The term F-Center comes from the German word farbe, which means "color." F-Centers are responsible for coloring a variety of minerals, including fluorite and barite. In hackmanite, it is proposed that some of the negatively charged chlorine atoms are missing. A negative electric charge is required at such vacancies to provide charge balance, and any free electrons in the vicinity become drawn to such vacancies and are trapped there. Such a trapped electron is the typical basis of an F-Center. It appears that this center in hackmanite absorbs green, yellow, and orange light and varying amounts of blue. When the hackmanite is seen in white light, red and some blue are returned to the eye, giving the hackmanite colors. It is likely that sulfur, as double negatively charged disulfide units S22-, is the source of the electrons. When ultraviolet is directed at the sodalite, it is absorbed at disulfide units. These each lose an electron and thus become S21- units. The free electrons wander to the chlorine vacancies where they are trapped, coloring the mineral."
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Rob Woodside September 26, 2009 07:17PM
Thanks Fred. Yes our posts crossed during edit and I'm surprised that your CFL didn't have enough UV to over come the bleaching. Yellow starts at roughly 5900 A and 4800 A is well into the green, almost blue. These are the wavelengths Medved says are best at bleaching. The wavelength or colour of course gives you the energy available (photon) for mucking about with the electronic structure and the intensity of the light tells you the sum of these available energies. So I suspect that the difference caused by your CFL sources arose more from intensity rather than wavelength.

I don't think this is a finished story yet. What you quote from Robbins seems to me the kind of sensible story containing several truths that I fall into, defend vigorously, and then realize that reality is a little more complicated. My recent posts on agates, nepheline, and dauphine twinning are good examples, in case anyone is counting. One problem here is that colours are often determined by minute traces of things that are undetectable with standard methods. I have several probe spectra (EDS) of colour changing Hackmanites that detect no sulfur. Certainly polysulfide is responsible for the ultramarine of Lazurite and this suggests to people that sulfur may have a role in Sodalite/Hackmanite. It may. However in spite of their peccadillo of Native Sodium, Annersten and Hassib show that the absorption at 5300 A is a F centre and supposedly responsible for Sodalite's blue colour, whereas the much broader absorption at 5800 A is not an F centre and seems responsible for the fading pink colour of hackmanite. Yet both are caused by ionizing radiation. All sodalites can be heat bleached to a grey white that can be recoloured by ionizing radiation. So finding a grey white sodalite means either that it experienced high temperature or there was insufficient ionizing radiation present to colour it. As James Hutton pointed out so long ago, the same tiny changes occurring over vast times can produce large changes and Reiner is quite right about waiting long enough to see radiation induced changes in Hackmanite. Until these absorption bands in sodalite/hackmanite are completely understood I don't think anything is certain.

I don't know if Medved introduced the word tenebrescence, but he says it comes from the Latin tenebrae for shadows and has a diagram to explain it. The formating gets screwed up on posting so I'll describe it. He starts with a clear xl and bombards it with x-rays, electrons, etc. that turn it into a coloured xl and then reverses the colour change with exposure to heat, light etc. So this tenebrescence is very broad and would include thermoluminescence etc. Today the preferred term is photochromic which as far as I can find merely means a reversible colour change caused by light. This narrows things somewhat and would seem to include fluorescence, phosphoresence, and darkening or bleaching caused by light. The new sun glasses darken in the presence of light and bleach in its absence, but hackmanite actually darkens in UV rich light and bleaches in visible light!!!



Edited 1 time(s). Last edit at 09/26/2009 07:22PM by Rob Woodside.
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Rob Woodside September 26, 2009 07:42PM
To back up my claim that some gemmy blue sodalites darken on UV exosure, here's the proof:


Gemmy blue sodalite before and after a short UV exposure



As far as I can tell this change is permanent!!!
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Reiner Mielke September 27, 2009 01:28AM
I am repeating my experiment with uraninite. This time I have a control sample. I found two pieces of bleached hackmanite of approx. equal tenebrescence ( you can determine this with long wave UV because tenebrecent hackmanite fluoresces more brightly than non-tenebrescent hackmanite). See attached photos. I then wrapped one with a piece of uraninite in lead sheet and the other by itself in aluminum foil and placed them about 20cm apart. I am now going to wait for a couple weeks and then photograph the two samples again to see if there is any colour change. I am betting that there will be a colour change in the sample with the uraninite. Stay tuned.
open | download - Hackmanite White.jpg (412.1 KB)
open | download - Hackmanite LWUV.jpg (425.8 KB)
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Rob Woodside September 27, 2009 06:35AM
Thanks Reiner. I hope your Uraninite is a bloody hot Precambrian one and that the hackmanite turns blue in a few weeks!!! However it may take much longer for anything to happen. The question that is driving me nuts is whether the hackmanite that shows fading pink on fracturing is actually pink on the inside??? I suspect it is not and the pink colour is actually caused by the fracturing. I don't know of any stong chemicals that would strip the surface faster than it would fade, but a chemist might suggest how to quickly chemical mill hackmanite. If it really is due to the fracturing then if two pieces of bleached pink fading hackmanite were bashed or harshly rubbed together fracturing powder from the surface then we should see some pink in the powder This would be triboluminescence that happens with some quartz and sphalerites. Could you please try that and tell us what happens?

Here's a picture of my hackmanite that has dark adapted for over 6 months and contrary to Medved's report has not recovered any of it pink color.


Dark adapted Hackmanite




Fred says his St Hilare Hackmanite fades in sunlight. Here's what happens to my dark adapted Hackmanite with a 10 minute exposure to direct sunlight. It clearly doesn't fade!!!


Dark adapted Hackmanite after a 10 minute direct sunlight exposure




A 10 minute exposure to UV makes it pretty dark purple


Purple Hackmanite caused by a 10 minute UV exposure





This purple Hackmanite was then left under a Tungsten source for 2 hours and it bleached considerably. Now it is only slightly pinker than the dark adapted example


After 10 minute UV exposure and then 2 hours under a tungsten source.




Now the tungsten source exposed Hackmanite is given another 10 minute UV exposure to restore the purple colour


After bleaching the purple Hackmanite returns with a 10 minute UV exposure




Now the UV exposed Hackmanite is left in the dark for 2 hours and only some of the purple fades


Faded colour after a 2 hour dark adaption




From these data one can conclude:

1) Exposure to ultra violet rich light causes very slowly fading absorption bands that don't absorb the pink/porple colour of this Hackmanite

2) The destruction of these adsorption bands be speeded up by exposure to light poor in ultra violet



Edited 4 time(s). Last edit at 10/21/2009 11:57PM by Rob Woodside.
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Reiner Mielke September 27, 2009 07:44PM
Hello Rob,

I will powder a piece of faded tenebrescent hackmanite in the dark and let you know what happens. Have to be carefull not to powder it too much, since it has a white streak, even bark blue sodalite powders white. My Davis quarry hackmanite behaves the same as your St.Hilaire stuff. So much for the darkening in the dark theory. The last time I experimented with uraninite/hackmanite there was a noticeable colour change after 3 days so three weeks should produce a good result. The challenge will be photographing it, I will have to do it in the dark with a flash. Good thing it doesn't fade instantaneously or we would be caught in the fridge door light conundrum.

Reiner
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Reiner Mielke September 27, 2009 08:10PM
Just a thought. Maybe the tenebresecent coloured hackmanite is " born" (formed) coloured and exposure to any light destabilize this primary colour causing it to fade in the dark from that point on. However I still think that radioactivity is what colours it so that once you take it away from a radioactive source it fades in the dark. That would mean that if I break open a large faded chunk of hackmanite that has been in my basement for a long time it should be white inside. When I broke open large chunks at the quarry they were coloured inside. I will try smashing open a large faded chunk (11kg) that I have and see if it is coloured inside. Hate to do it though after lugging it 4km on my back so I could have a big piece, oh well I'll do it in the name of science.
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Reiner Mielke September 27, 2009 08:39PM
Broke open the large chunk and it was coloured on the inside (that is at the core but white from the outside to a depth of about 5cm). Originally when I found it it was coloured on the outside. My head is starting to hurt! 8-) If the force of fracturing induces a colour wouldn't one expect the colour to be all along the fracture surface and not just at the core? If radioactivity preserves the colour why didn't it fade evenly in the dark when taken away from the radioactive source ( in the Davis Quarry that would be radioactive zircons). At this point the only thing that fits this data is the birth-colour destabilization theory. In otherwords since the core of the sample has never been exposed to light of anykind the colour is stable. However since the outside has been exposed to light ( it would seem to a depth of 5cm) the colour is not stable and fades in the dark. Anyone else have an explanation?
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Fred E. Davis September 27, 2009 09:15PM
I took a quick peek at the spectrum of the bright-white CFL, and found strongest peaks around 5500 A and 6300 A. There are less intense peaks around 4400, 4900, 6000 and 6600 A.

Manuel Robbins suggests the range 4800 to 7200 A is best for bleaching.

As with many things, there's a lot of wiggle room. :)
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Reiner Mielke September 27, 2009 09:20PM
Hello Fred,

Thanks for the info, I found that CFLs work well for bleaching but you still have to keep the sample in the dark afterward to get it to bleach completely, at least for Davis Quarry stuff.

Reiner
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Fred E. Davis September 27, 2009 09:25PM
Yup, Robbins mentions a lot of variability. Some do, some don't. Go figure...
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Jan Styer-Gold October 06, 2009 04:17PM
Here's another one to add to the list:

Chrysoprase (Chalcedony) (light green to apple green)

The color of chrysoprase can fade in sunlight and when heated. The color may return if the specimen is kept under moist storage away from light.

Jan
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Alfredo Petrov October 06, 2009 05:23PM
With regard to the chrysoprase (and other chalcedony varieties); This is probably not a true colour change, but rather decreased transparency caused by evaporation of interstitial water in micropores. The colour "returns" when you get it to absorb water again.
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Anonymous User October 06, 2009 05:46PM
Pink Halite from Searles Lake. Sunlight kills the salt loving bacteria that cause the pink colour.
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Anonymous User October 07, 2009 06:17AM
Tourmaline is not photosensitive. Tourmaline is typically heat sensitive, and the color can be lightened by exposure to intense heat. This is usually done to tourmaline that has been artificially irradiated to produce a dark red color, which then can be heated to lighten the hue, and produce a lighter hued reddish pink. Heat treatment can also be performed on dark bluish green tourmaline to lighten the hue. Heat treatment, however, is not the same thing as photosensitivity. I am unaware of any tourmaline species fading from exposure to near infrared, visible, or ultraviolet light - which includes examples that have been artificially irradiated and/or heated to change the color. The color center is always stable. The only portion of the electromagnetic spectrum that has an effect on tourmaline is gamma rays and x-rays, and this exposure causes a increased saturation of color, versus fading, or desaturated color.
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Adam Kelly February 28, 2010 01:10AM
Does anybody know?
Is the fluorite from Riemvasmaak, Northern Cape Province, South Africa prone to fading in sunlight?
This local is sometimes called Orange River also.
AK
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Rock Currier February 28, 2010 03:48AM
It may be since this is a relatively new locality that there has not been enough time pass yet for it to be known if the color will fade yet. If a dealer gets an exciting new find of a mineral, usually one of the bottom of the list things he wants to do is to take matching pieces of the mineral and place one of them in strong sunlight for a month so he can report on any color fading. There is no financial upside in this sort of experiment, only a potential down side. If however a competitor starts a roomer that the color is not stable, which happens quite often, so as to hopefully dampen the sales of a competitor, then such a text will be done as quickly as possible so that damage control can be instituted.

Rock Currier
Crystals not pistols.
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Adam Kelly February 28, 2010 09:14PM
Thanks Rock,
Thats pretty much what I figured.
My girlfriend works in a rockshop.
Her boss just brought back a few pieces from Tucson.
The front window in the shop gets lots of sun, and thats where they are right now.
It's worth it to me, just to help preserve minerals in their prime condition.
Thanks,
AK
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Luiz Alberto Dias Menezes, Fo. March 01, 2010 12:03AM
One of the most dangerous minerals in terms of color decaying under light is pink apatite; my experience with pink apatites from at least 2 Brazilian localities (Morro Velho gold mine and Golconda mine) is that under sunlight the pink color fades completely in no more than 30 minutes. At the 2008 Sainte Marie aux Mines show I lost several specimens because the sides of my tent get exposed to sun-light and so I was trying to keep the flat with the pink apatites away from it but customers handle the flats back and forth and somebody moved it to the wrong place so in minutes the pieces lost the pink color.
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Rock Currier March 01, 2010 02:50AM
Luiz,
I was once told that these apatites can be irradiated and made pink again. I have also experienced some color loss with my Morro Velho apatites even though they have mostly been kept in the dark.

Rock Currier
Crystals not pistols.
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Alexandra Catalina Seclaman March 02, 2010 07:13PM
Someone said amethyst is light sensitive?

I have a piece since i was born and it has the same color, and it gets a lot of light.
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Rock Currier March 02, 2010 08:25PM
The amethyst from Rio Grande do Sul and that from Artigas Uruguay are slowly light sensitive. The fading is not something that is immediately apparent, but if you put them out in direct sunlight for six months, the fading is very obvious. All the guys who work with amethyst at those two localities know this and I have run exposure tests on specimens from both localities. I have not run tests on amethyst from other localities, but I suspect that amethyst from other localities will also fade. To test the amethyst from a locality you need two more or less identical specimens. One you put in a dark place and the other you put out in your garden for a few months and at the end of the time you compare the two specimens. Very simple. But who wants to do these tests when the best you can discover is that the specimens from a locality will not fade. Since I have never heard any amethyst suppliers boast that their amethyst is stable, I assume that if such tests have been made, the results have shown that the amethyst fades and that fact is kept quiet.

Rock Currier
Crystals not pistols.
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Rob Woodside March 02, 2010 08:43PM
Somewhere I saw a photo of an amethyst xl specimen that had be broken in half and re-assembled. One half was a satisfying dark amethyst and the other half a sickly weak amethystine quartz. One half had been left in full sunlight for sometime and the other half kept out of direct sunlight.

I would be surprised if some amethysts lightened and others did not. I rather suspect that the darkest ones lighten at a slower rate
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Rock Currier March 02, 2010 09:35PM
Rob,
That would probably be the picture of a specimen of amethyst from Rio Grande do Sul that I made and was published in Gems and Gemology showing a specimen of amethyst that I broke in half. One half I put in the sun for about six months and then glued back together with the piece that had been in a dark box for the same length of time.

Rock Currier
Crystals not pistols.
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Rob Woodside March 02, 2010 10:50PM
Rock, that was a great photo of a very sick rock. ( BTW I hope your Tucson cold is better now. Luckily I seem to have escaped its clutches) If you have access to that photo, could you possibly post it here?
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Rock Currier March 03, 2010 08:06AM
Bob,
Im sure glad you didn't get my cold and managed to escape the clutches of the Tucson International Viral Distribution Center. Usually I don't manage to escape. But its all better now and I am back working hard to try and finish the scanning in of the balance of my specimen images. Then I will have the tedious job of photoshoping them all in preparation to uploading them to Mindat. Just took delivery today on my second batch of compressed air in a can (30 bottles at about $100). This should see the job of blowing the dust of the slides to an end. Do you know anyone else who has spent $200 just to blow the lint off their specimen images? Sometimes I think I feel reality slipping away from me.

I took a quick look for that image of the two tone amethyst, but could not locate it. It should be here somewhere in my 50 to 100 K 35mm slides, but other than mounting a month long search effort I think I will just wait till it shows up. When it does, Ill put it in the article I just finished about amethyst.

Rock Currier
Crystals not pistols.
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Edgars Endzelins June 14, 2011 09:23PM
Anyone knows if lorandite is light sensitive? I recently aquired one and noted that crystals on back side of specimen shows more luster but on front side are rather dull...
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Antoine Barthélemy December 31, 2014 10:09AM
I am somehow disappointed by the large number of species listed on page 4 in this topic. Also, although nothing new was posted here for quite a long time, I am always afraid that species I have on display will once appear on such a list.

So here is my question: are there really light insensitive species ? Azurite, dioptase or pyromorphite (for instance) are never listed as light sensitive minerals. Does it mean that I can let them on my shelves (sometimes exposed to sunlight) without any harm ? Or would you think that it is anyway better to have the display shelves kept in the dark ?
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Alfredo Petrov December 31, 2014 10:37AM
I wouldn't worry about it too much, Antoine. The list you refer to has about 70 species on it (out of the 5,000 or so known mineral species), and for most of those 70 species it is only certain varieties that suffer in the light, not all samples of the species. And some of the things on the list I simply do not believe at all... blue sodalite, light sensitive? Not in my experience - I've had blue sodalite in a sunny window for 20 years and it's still blue.

There are of course some species I would not display in bright light: several noriously sensitive silver and mercury minerals, realgar, vivianite, coloured topaz, purple apatite, amethyst... and a few more, but I'd probably only have 30 species on the list rather than 70.
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Reiner Mielke December 31, 2014 01:34PM
Hello Rock,

"my second batch of compressed air in a can (30 bottles at about $100). This should see the job of blowing the dust of the slides to an end. Do you know anyone else who has spent $200 just to blow the lint off their specimen images?" Wouldn't it have been cheaper to buy an air compressor?
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David Von Bargen December 31, 2014 02:24PM
"Compressed air" is most often tetrafluoroethane. When you use an air compressor, unless you filter it, you will just be blasting dust in the air at your photos. You might also be adding some lubricating oil to the air stream.
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Reiner Mielke December 31, 2014 02:36PM
Yes I would recommend filtering it. The big advantage to compressed air is not only cost but you can use the compressor for other things when you aren't blowing away dust.
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Jakub Jirásek December 31, 2014 04:09PM
Also many hydrated sulfates, since light means energy convertible to heat.
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Rob Woodside December 31, 2014 04:32PM
Alfredo, the recently found gem blue sodalites with Wurtzite become darker and turbid underv UV
http://www.mindat.org/photo-253461.html
The usual translucent blue sodalite from everywhere else is either totally stable or has already darkened.
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Vitaliy January 01, 2015 07:29PM
Is Russian Cuprite (particularly from Rubtsovskoe Cu-Zn-Pb deposit, Rudnyi Altai, Altaiskii Krai, Western-Siberian Region, Russia) also affected especially the ones that backlight red? I was under the assumption it was for the more translucent red Cuprite crystals encountered from other localities.
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Alfredo Petrov January 02, 2015 12:34AM
In the case of cuprite, is the darkening really a light-stimulated change, or is it a tarnish caused by reaction with traces of sulphur in the air?
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Doug Daniels January 02, 2015 02:07AM
Alfredo - possibly a combination of the two?
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Vitaliy January 02, 2015 02:12AM
Alfredo Petrov Wrote:
-------------------------------------------------------
> In the case of cuprite, is the darkening really a
> light-stimulated change, or is it a tarnish caused
> by reaction with traces of sulphur in the air?

Has darkening actually been proven to occur on Cuprite's especially those from Rubtsovskoe. I haven't actually seen any actual evidence or facts that show Cuprite darkening from that locality. I can understand it possibly occurring on Translucent Red Crystals from other localities.

The darkening itself has been rumoured to be caused by exposure to either Sulphur in the air (from decomposing Pyrite crystals was mentioned) or simply the exposure to UV or daylight.
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Alfredo Petrov January 02, 2015 03:00AM
Inside houses, there is always some sulphur in the air, even without the presence of pyrite. Cooking eggs, cabbage and other vegetables in that family, city air pollution, and... ahem... (how to put this delicately?) sulphur-bearing vapours emitted by homo sapiens and their domesticated animals... = tarnishing of silver and copper minerals.
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Vitaliy January 02, 2015 03:03AM
Alfredo Petrov Wrote:
-------------------------------------------------------
> Inside houses, there is always some sulphur in the
> air, even without the presence of pyrite. Cooking
> eggs, cabbage and other vegetables in that family,
> city air pollution, and... ahem... (how to put
> this delicately?) sulphur-bearing vapours emitted
> by homo sapiens and their domesticated animals...
> = tarnishing of silver and copper minerals.

How much of it is present compared to decomposing or decaying Pyrite that we might have in our collections. I would think that a decaying Pyrite would give off more Sulphur than simple background 'sulphur' if we can call it that. There are also other minerals that decompose and produce Sulphur as a result.

I personally don't mind tarnished copper or silver. I feel it gives it an older 'old world' look to it.
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Rob Woodside January 02, 2015 04:44PM
Why isn't the black that forms on all cuprite, just tenorite? Has anyone analysed the scuzz?
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Rock Currier January 03, 2015 05:31PM
Yes, it might have been cheaper to buy a compressor, but when I started the job I had no idea of how much compressed air it would take and by the time I did, it didn't seem worthwhile to fool around with a compressor,hook it up and then have an extra hose running into my office plus a switch to turn it on and off when I needed it and then to wait for the pressure to build up. It was faster to just be able to pick up a can close at hand and work with it. I figure the electricity and especially the time saved was worth the expense. I didn't even have to buy a compressor. I could have just taken one from my place of business as I had several extra ones. I also din't like the idea of having one making noise all the time hammering away to fill its little tanks. Then there was the problem that I would have to probably filter that compressed air and periodically drain water from the tanks and maintain the damn thing.

Rock Currier
Crystals not pistols.
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Sans March 13, 2016 06:15PM
Hi, I just recently purchased a beautiful specimen of dioptase and a specimen of aragonite from northern lights mine nevada and I was wondering if anyone could help me figure out if they are light sensitive? I took a look at the list but I am unsure if my aragonite qualifies as colourless or not.
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Alfredo Petrov March 13, 2016 07:13PM
Shouldn't be any problem with either dioptase or colorless aragonite.
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Robin Ball July 01, 2017 08:54PM
List of photosensitive minerals please so I know what stones to keep out of the sunlight. Besides rose quartz.
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Reiner Mielke July 01, 2017 09:04PM
A follow up on the Davis Quarry hackmanite. My hackmanite specimens have changed their habit? Now they behave like normal hackmanite in that they retain their color in the dark but fade in the sunlight? Seems the material only exhibits the opposite reaction for a limited number of times. Very strange.
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Alfredo Petrov July 01, 2017 09:08PM
"Besides rose quartz."
Robin, normal rose quartz (the massive kind) is one of the minerals that is not light sensitive; only the crystals of rose quartz (aka "pink quartz") will fade in the light.
And keep in mind that light sensitive minerals won't only fade in sunlight, but in artificial light as well, albeit perhaps slower since the light is usually less intense.
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Jolyon & Katya Ralph July 02, 2017 12:05AM
I had a light-sensitive mineral list, but it faded.
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Robin Ball July 02, 2017 02:41AM
List of photosensitive minerals please so I know what stones to keep out of the sunlight. Besides rose quartz.
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Alfredo Petrov July 02, 2017 04:38AM
amethyst, colored topaz, realgar, kunzite, purple apatite...

plus many silver and mercury minerals (eg: proustite, chlorargyrite, and many more, although most of them are rare and you probably don't have any anyway)
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Stuart Herring July 02, 2017 10:24PM
Some fluorite's like Blanchard NM
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