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How common is pyrite disease?
  
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protium




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PostPosted: Sep 19, 2017 17:30    Post subject: How common is pyrite disease?  

Being very new to collecting, every time I bring a new specimen home I do some research on it. While looking into pyrite I came across pyrite disease, which I have also heard referred to as pyrite rot.

How common is this for a specimen kept in average humidity. It can occasionally become fairly humid here in the summer, but usually, humidity is low.

Are there any recommended preventative measures that can be taken? I read of one man that swore by coating the specimen in sewing machine oil. At the moment the nice little twinned cube is in excellent condition. It has a consistent metallic luster, with no discoloration.

I am also wondering if chalcopyrite can suffer the same fate?

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Richard
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Pete Richards
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PostPosted: Sep 19, 2017 17:57    Post subject: Re: How common is pyrite disease?  

Pyrite disease is universal. It is the natural drive for oxygen to interact with the iron sulfide that is pyrite and break it down to iron sulfate, which is a powder and which will expand in cracks and tiny pores and break the specimen apart.

It happens at different rates in different specimens for various reasons.

It affects almost all (maybe all all) metallic sufides, at different rates.

A good start to understanding this problem is at this site in this forum: http://www.mineral-forum.com/message-board/viewtopic.php?t=2498

No rush - you have a few months, at least. But as soon as possible get the specimen dry and isolate it from oxygen and changes of air.

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protium




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PostPosted: Sep 19, 2017 21:53    Post subject: Re: How common is pyrite disease?  

Thank you for the quick response, I will try to find a suitable vessel for them as soon as possible. I was hoping I was worried about nothing, but I would rather be safe than sorry.

From reading the thread you linked to this problem seems very unpredictable.

Richard
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Pete Modreski
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PostPosted: Sep 20, 2017 13:14    Post subject: Re: How common is pyrite disease?  

Richard, just to add, I think you'll find that pyrite nodules that form in sedimentary rocks, tend to be the most susceptible to rapid deterioration. Most of the "very clean looking" pyrite specimens that come in large crystals from ore deposits, such as the pyrite from Peru or from Gilman, Colorado for example, seem to be completely stable, at least over the lifetime of specimens in a museum or in one's collection.
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Roger Warin




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PostPosted: Sep 20, 2017 16:31    Post subject: Re: How common is pyrite disease?  

Hi,
Several answers, including Pete's, explain the problem of this corrosion.
I would like to add a remark. Some pyrites are very stable, others not.
I think we have to look at an electrochemical aspect. When there is an impurity, for example marcasite, a very probable hypothesis, a difference of potential is created in the crystal similar to that which appears in an electric cell. The redox reaction becomes inescapable especially in the presence of moisture. The potential does not give rise to light, because the connections have not been made, but the reaction occurs with a slight release of heat to give the various sulphates. The crystal undergoes gangrene. Nothing stops it as long as the chemical balance is not reached. In the case of the electric battery, it is flat. The crystal also.
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protium




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PostPosted: Sep 20, 2017 19:02    Post subject: Re: How common is pyrite disease?  

Thank you for all the responses. I am a bit torn, the iron pyrite does smell faintly of sulfur, the chalcopyrite less so but it is still there. On the one hand, I would like to ensure both are preserved. I am considering tiny bell jars that could be sealed.

On the other hand, neither was particularly expensive and it would be nice not to have to view them under glass. Unfortunately, I have no way to determine the exact chemical makeup of either specimen. I am a little more concerned about the chalcopyrite, it is laced with both relatively large and very fine siderite crystals. I quite like that one...

I will probably just get a few bell jars and see how I like the look. After all, what is the point of collecting minerals if I can't enjoy them?

Richard
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Pete Richards
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PostPosted: Sep 20, 2017 19:17    Post subject: Re: How common is pyrite disease?  

A much cheaper alternative - get a batch of 8 oz or 4 oz jelly jars and put the specimens in them. The lids that come with the jars will seal the space inside and prevent incursion of new oxygen. If you look at the specimens two or three times a year, you will let in a bit of new oxygen, but it will be minescule compared to what would occur with the specimen sitting in an open drawer or on a shelf.

If you're worried about the fact that you already smell "sulfur" [probably either hydrogen sulfide (rotten eggs) or sulfur dioxide (burned matches], you could try heating the specimen gradually in an oven to 300° or so to kill the sulfur bacteria that facilitate pyrite decay.

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