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Loss of luster on russian cuprite
  
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bob kerr




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PostPosted: Nov 23, 2014 16:47    Post subject: Loss of luster on russian cuprite  

I may be imagining it but I think a few of the Rubtsovskoe cuprites I bought two years ago and have been on display since then have seem to have lost a bit of their luster. I do not have good enough original photos for comparison - so just a generic question - can light exposure and or moisture exposure or anything else dull the luster of these cuprites?

thanks,
bob
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Bob Carnein




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PostPosted: Nov 23, 2014 18:12    Post subject: Re: Loss of luster on russian cuprite  

Do you happen to have any pyrite nearby? Fumes from alteration of pyrite sometimes attack the luster of nearby minerals.
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PostPosted: Nov 23, 2014 20:59    Post subject: Re: Loss of luster on russian cuprite  

the cuprites are in a display of other copper based minerals and native coppers.

there are pyrites on another display shelf some distance away and I kinda think the luster on these (mainly from Peru) may be suffering also.

bob
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PostPosted: Nov 23, 2014 23:43    Post subject: Re: Loss of luster on russian cuprite  

I have noticed the same thing - one of my cuprites "fogs up." I can clean it with soapy water and a tooth brush to a brilliant luster, but then after several hours it fogs up again. This same cuprite also has what looks like a permanent finger print that I can't clean off with simple soapy water. I have made sure that no soapy residue stays on the piece - I use a simple dish soap (no fragrances, anti-bacterial, or other crap), rinse it thoroughly under running water, and wipe/polish it dry with a clean rag. Our water here is mostly surface water from a melting glacier - very low in dissolved material.

This cuprite is stored in its own box, wrapped in plastic. Any nearby pyrite is also wrapped in plastic in its own box. I don't know how it was stored before i bought it.
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PostPosted: Nov 24, 2014 06:07    Post subject: Re: Loss of luster on russian cuprite  

bob kerr wrote:
there are pyrites on another display shelf some distance away...

Matt_Zukowski wrote:
This cuprite is stored in its own box, wrapped in plastic. Any nearby pyrite is also wrapped in plastic in its own box.

Relative distance and wrapping could be not definitive because the problem of some Pyrites (not all Pyrites, the Spanish ones from Navajún for example don't create troubles) are the vapors that they could liberate (humidity H20 + S02 sulfur dioxide vapors liberated for the pyrite = S04H2 sulfuric acid) that even in very weak quantity can, after a while, do some kind of attack to some other sensitive minerals.

Anyway, the Cuprite by itself is also very sensitive to the sunlight...
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Pete Richards
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PostPosted: Nov 24, 2014 08:20    Post subject: Re: Loss of luster on russian cuprite  

Cuprite is a fairly reactive mineral. It alters to malachite, native copper, and various other copper minerals. It is attacked by most acids, including sulfuric acid, according to Dana's System 7th edition. Pyrite decay produces sulfuric acid.

That said, most of this mineral hanky panky occurs in a liquid or at least moist environment, and it is harder to see how it would occur in a dry display case. The pyrite might be releasing some sulfur dioxide, but how much damage it would do at a distance of multiple feet in a dry environment is uncertain.

A useful question is whether you have other cuprite specimens which have had a different storage history, and whether they are also losing luster. Another useful question is how sure you are that your specimens are losing luster. Does time make the (remembered) luster grow brighter over time? I think of the fisherman whose catch grows a bit bigger each time he tells about it over the years!

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alfredo
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PostPosted: Nov 24, 2014 08:47    Post subject: Re: Loss of luster on russian cuprite  

Just a guess: Could traces of H2S gas be causing tarnish just like happens on silver cutlery? If so, the tarnish is likely to be chalcocite, an unstable sulphide that rapidly turns dull. That would explain why the tarnish takes a polish but rapidly gets dull again.
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Peter




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PostPosted: Nov 24, 2014 09:55    Post subject: Re: Loss of luster on russian cuprite  

Yes, as Jordi mentions, Cuprite is light sensitive. Keep it out of daylight, I keep it in my dark mineral room! Where the light is only on when I am there.

Of course do not keep marcasite-pyrite even nearby.

I must also add the environment where you live i.e. air pollution!

A small silver from Kongsberg had little patina living in Sweden for many years. Moving to a house where each house has its own heating system burning fuel certainly has not been positive for the silver i.e all black now!
Peter
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John Betts




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PostPosted: Nov 24, 2014 22:14    Post subject: Re: Loss of luster on russian cuprite  

Are you storing the cuprite in oak cabinets?
Oak has tannic acid that affects books, so the cuprite might also...

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Martin Rich




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PostPosted: Nov 24, 2014 22:31    Post subject: Re: Loss of luster on russian cuprite  

[....humidity H20 + S02 sulfur dioxide vapors liberated for the pyrite = S04H20 sulfuric acid....]

Sorry Jordi, the formula for sulfuric acid is H2SO4.
Anyway, sulfurous acid (H2SO3) is also possible. If you are living in a town or in an industrial area, H2S is in small amounts omnipresent and this chemicals may affect some minerals.

Martin

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Roger Warin




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PostPosted: Nov 24, 2014 23:19    Post subject: Re: Loss of luster on russian cuprite  

Hi,
Red cuprites should not to be exposed to light. Light catalyzes perhaps this reaction between the H2S acid and the basic oxide copper.
The ambient level of hydrogen sulphide is estimated at 0.3 g / m³ of air. This level increases in industrial zones and polluted areas also by decomposition of organic origin.
There is another fact.
Copper is monovalent in Cu2O. Compounds wherein the copper atom is monovalent are easily oxidized to cupric derivatives, often by simple exposure to air.
Therefore, we must keep the red cuprites under nitrogen or at least in dry air.
This explains the remark of Peter on the loss of air quality in Luxembourg compared to Sweden. Silver suffered the same fate.
Belgian collectors do not exhibit the Katanga red cuprites in showcases.
Roger.

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Jordi Fabre
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PostPosted: Nov 25, 2014 02:23    Post subject: Re: Loss of luster on russian cuprite  

Martin Rich wrote:
[....humidity H20 + S02 sulfur dioxide vapors liberated for the pyrite = S04H20 sulfuric acid....]

Sorry Jordi, the formula for sulfuric acid is H2SO4.

Sure Martin, a typo error. I already fixed it.

Thanks for the warning!
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bob kerr




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PostPosted: Nov 25, 2014 11:36    Post subject: Re: Loss of luster on russian cuprite  

thanks for the numerous responses.

I agree about the sunlight issue - for essentially ALL specimens - so my cabinets are very shaded (never in sunlight) and only in light when I turn on the LEDs. I don't think exposure to light is the cause.

the cabinets are made of pine which is painted - not sure if that would be the culprit.

the discussion on air pollution and gases from pyrites are possibilities. I may start storing pyrites away from everything - as their luster seems to be fading also.

living in western PA - with all the summer time humidity - this is possibly the main culprit - especially this last summer. the house humidity is certainly lower than outside but a far cry from Tucson.

I tried the soap/water/toothbrush idea and the luster got a bit better. I've attached a before and after - not too much difference. note the flattened luster although the luster is still ok. for scale - the acrylic base on the right is 3.2cm (1 1/4 inch).

thanks again,
bob



cuprite before.jpg
 Mineral: Cuprite
 Locality:
Rubtsovskoe Mine, Rubtsovsky District, Altai Krai, Russia
 Description:
before soap/toothbrush cleaning
 Viewed:  21260 Time(s)

cuprite before.jpg



cuprite after.jpg
 Mineral: cuprite
 Locality:
Rubtsovskoe Mine, Rubtsovsky District, Altai Krai, Russia
 Description:
after a brief soap/toothbrush cleaning
 Viewed:  21293 Time(s)

cuprite after.jpg


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Vitaliy




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PostPosted: Dec 02, 2014 18:31    Post subject: Re: Loss of luster on russian cuprite  

I have not really noticed a significant difference in the loss of luster of my Russian Cuprite's either. They are not directly exposed to the sun or light whenever it shines but are not in a dark or enclosed box either for the ones that I have just checked on.

As some have said the Cuprite specimens that backlight Red are more sensitive than the opaque specimens that are commonly encountered. Russian Cuprite usually do not backlight red except perhaps on the edges or on the more translucent specimens.

I also doubt that Pyrite specimens that are in a state of 'Pyrite Decay' would directly attack it unless they are a concretion. Most Pyrite specimens are relatively stable from various localities. The sandstone pyrite concretions or Pyrite concretions are the ones to watch out for when storing it close to other specimens.
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