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"Pyrite Disease"

Posted by Robert Simonoff  
Robert Simonoff August 19, 2009 02:54PM
Hi everyone,
A while ago I went collecting with a club and found some nodules of pyrite or marcasite. They are beginning to catch "pyrite disease," cracking and crumbling. Will putting them in a closed box so that they are exposed less to sunlight help prevent further cracking and crumbling? Is there anything else I can do to prevent cracking/crumbling?
Alfredo Petrov August 19, 2009 03:21PM
I don't think light has anything at all to do with it. A closed box isn't going to help unless you have a dessicant in it too. Extreme dryness will help slow the decomposition.
Robert Simonoff August 19, 2009 04:13PM
Thank you Alfredo, that was a very quick response! :)
What is a dessicant, and how do you achieve extreme dryness?
Chris Stefano August 19, 2009 04:22PM
silica gel packets that you get with shoes and other such materials are dessicants- they absorb water from the air. A dehumidifier can be used to maintain dryness as well.
Robert Simonoff August 19, 2009 04:27PM
Oh I see, thank you. Now I will have to try to find at least one of those silica gel packets I saved up for various science experiments and the like... ;)

Edited 1 time(s). Last edit at 08/19/2009 04:27PM by Jessica and Robert Simonoff.
Barry Flannery August 19, 2009 04:41PM

I think that you will find that you need more than just a single packet. Also remember that the piece will have to be kept in an airtight container to prevent constant refreshment of humid air. The silica gel can only absorb a certain amount of water before becoming useless. At this stage it is useless.

Alfredo Petrov August 19, 2009 04:48PM
I use the calcium oxide (lime) packets that come with japanese seaweed. I think it's a more aggressive dessicant than silica gel.
Barry Flannery August 19, 2009 04:59PM

What do you think the effects of keeping a specimen under a nitrogen atmosphere or a noble gas would be? Of course keeping it dry at the same time. I was thinking that perhaps the nitrogen would inhibit the respiratory functions of the thiobacillus ferrooxidan bacterias?


Edited 1 time(s). Last edit at 08/19/2009 04:59PM by Barry Flannery.
Robert Simonoff August 19, 2009 05:11PM
How often should I change the silica gel pouches? (I don't have calcium oxide like Alfredo gets)
Ian Jones August 19, 2009 05:21PM
just gently reheat it to drive off the water, then it can be reused.
Alfredo Petrov August 19, 2009 05:30PM
Ian, won't the silica gel crystallize and then lose its hygroscopic properties?

Barry, you might be right; I haven't tried it.

Some museums use sophisticated vacuum techniques to suck out all moisture and then inject lacquer into deep cracks to prevent future decomposition. Seems like a lot of work for a mineral as common as pyrite. I'd rather just throw out the unstable ones and concentrate on finding relatively stable ones. Unfortunately, most lesser preservation efforts seem to only slow the process down but not stop it completely.
David Von Bargen August 19, 2009 05:30PM
There is also a desiccant that changes from blue to pink that can be regenerated by heating in an oven.

There are some chemical treatments that tend to inhibit pyrite disease, but they use some nasty chemicals and are often much more costly than the specimen is worth (mainly used on fossils). You should isolate these specimens from the rest of your collection.
Stephen Moreton August 19, 2009 06:02PM
Keeping the pyrite/marcasite dry is key to its survival. Water is essential for the reaction. As the reaction proceeds sulphuric acid is generated as a by-product. This is hygroscopic (absorbs moisture from the atmosphere) thus drawing in more water and causing more reaction. The reaction is therefore self-perpetuating and keeps on going until the pyrite is all consumed. From what I have read it seems unlikely that bugs, like T. ferroxidans, are involved, and may just be incidental, if present. Chemistry alone is probably enough. The finer grained, framboidal, pyrites are the worst, and I have seen many an example from the Irish zinc mines disintegrate. In fact so reactive is finely divided pyrite it has even been known to catch fire, as happened once in Tara mine, when a pile of such produced by drilling was left over the Christmas vacation, and ignited. To extinguish it that section of the mine was sealed to starve it of air. When everything had cooled down and it was re-entered the walls were coated with sulphur crystals distilled out of the pyrite.

As a research chemist for what used to be Europe's biggest desiccant gel manufacturer I am, perhaps, in a good position to figure out how best to keep my pyrites dry. Storing in a desiccator with a suitable desiccant, is my preferred method, but laboratory desiccators are big and expensive. Recently I have begun experimenting with cheap, plastic, air-tight food containers, which seem to be just as good. Fill them to about a fifth or a quarter of their volume (the more the better) with dry silica gel (can be in a sachet for convenience) and place the specimen next to it. There are many other desiccants available too. For very low humidities molecular sieves (zeolites) available as little grey pellets, are particularly effective, although I've found silica gel to suffice (at least my pyrites stopped falling apart once I began using it). Clay based ones are cheap, but generally not as good as silica gel. These can all be regenerated by heating, although zeolites need a good cooking at about 400 degrees C to get them really dry. Silica gel can be freshened in the kitchen oven at about 110 - 150 degrees C for an hour. Indicating varieties are available that change colour when used up. The traditional one uses cobalt chloride and turns from blue to pink. Turns blue again when baked in an oven to refresh it and can be used many times over. As cobalt salts are slightly carcinogenic I invented one based on iron which goes from amber to near colourless (United States Patent Application 20040209372). A variant I came up with later uses a Fe-bromo complex and gives a better colour change at even lower humidity and is manufactured under licence by Engelhard (as "Sorbead Orange Chameleon" ), although I am not sure if it is available to non-industrial consumers, but would be the best one for the job. Both can be refreshed in the oven many times over. Some people use a microwave oven, although temperature control is harder. There are other indicating silica gels, but those based on organic indicators (commonly blue/yellow colour change, although there are others) tend not to withstand many drying/redrying cycles. I have no qualms about using the traditional blue/pink cobalt-based one for my samples however, and it is probably still the most readily available. Just don't eat it!

As Alfredo says calcium oxide is an even more powerful desiccant (drying agent), however, unlike silica gel, it cannot be regenerated (except in a furnace). It is also very alkaline. Where I have found it useful, however, is in treating specimens in the early stages of pyrite rot. For this one needs a large air-tight container (a desiccator is ideal, although I guess a particularly large food box will do as long as it is air-tight). Fill a small beaker or pot (100 ml) with calcium oxide ("quicklime", best as lumps) and place it in the container. Place the specimens nearby in the container. Add a few ml of strong ammonia solution to the calcium oxide and put the container lid on fast. The calcium oxide reacts with the water in the ammonia solution, setting the ammonia free as gas. Leave for several days. Being a small molecule ammonia can penetrate into the tiniest spaces in the specimens, neutralising any sulphuric acid within them. It will thereby bring to a halt any pyrite rot, but will not repair the damage already done. Do this treatment in a well ventilated space (NOT in the house) as ammonia stinks. I use my garden shed. When done take the lid off (outside) and leave for 20 minutes for the smell to go then get the specimens into an air-tight container with desiccant as discussed above. If the specimen is already badly affected you may see some brownish colouration (hydrated iron oxides) where the products of the pyrite rot have reacted with the ammonia. In that form they will do no more harm, but rot will resume if the specimen is ever exposed to atmospheric moisture again, so keep it in its container and only bring it out briefly for ceremonial occasions.

Edited 1 time(s). Last edit at 08/19/2009 06:13PM by Stephen Moreton.
Robert Simonoff August 19, 2009 06:09PM
Thank you everyone! :)
Ben Kirchner August 19, 2009 07:35PM

Thanks that is a pretty interesting comment! I love hearing stories about mine fires. Do you know about the fire in Jerome, AZ? The sulphide body caught on fire, burned for about 30 years, and created a whole suite of interesting new minerals.. Pretty cool history! Thanks for sharing that all that information!

Ben Kirchner
Ray Hill August 20, 2009 07:37AM
Actually , it sounds like a pretty HOT history to me.
Thanks Stepen!
You and Alfredo always seem to come up with
interesting and thorough answers.
Rock Currier August 21, 2009 04:42AM
I think that is the best thing written to date on treating degenerating pyrite and Marcasite. Would you consider writing it up in a somewhat more formal sense for an article here on mindat. I would like to post it up in the welcome section of this forum to refer people to when they ask about this problem. If enough people address the more common aspects of cleaning and preparing mineral specimen, we will eventually have a pretty good manual for cleaning and preparation.

Rock Currier
Crystals not pistols.
Robert Simonoff August 21, 2009 06:00AM
Just a little clarification here. Are all FeSO family minerals at issue here? If I have a pyrite cube do I need to worry about it becoming a mineral killer? Or do I need to worry about that cube becoming FeO2 dust? Or are we really talking more about the forms witrh a very fine structure - very large surface area as in "The finer grained, framboidal, pyrites are the worst, and I have seen many an example from the Irish zinc mines disintegrate. In fact so reactive is finely divided pyrite "

Ralph Bottrill August 21, 2009 07:12AM
All iron sulphides are problematic. The worst specimens are probably fine grained or poorly crystalline sulphides, esp. pyrite and marcasite, because of the higher effective surface area. Most greigite needs immediate storage in nitrogen when collecting. The reaction often appears to start inside of specimens, which can eventually expolode - even well formed pyrite crystals can do this if they have framboidal cores. It has been found that inclusions of fine thiosulphate minerals can occur in some of these sulphides and I wonder if these unstable minerals can catalyse the reactions? Pyrrhotite is a common problem, because it often has some fine grained alteration to pyrite and marcasite. I understand a nitrogen or other inert gas atmosphere will work, as the reaction needs oxygen as much as water. Freezing of well-dried specimens is another technique I have heard of, to slow the reaction down. But once the reaction has started is is very difficult to stop it completely, without constant monitoring. Perhaps move to the desert?

Alfredo Petrov August 21, 2009 12:07PM
Pyrites decompose even in the driest desert on Earth, the Atacama, where there is still some moisture in the air, although I suppose pyrites do better in the desert than the jungle. But the most important thing collectors can do, especially in public display situations where it is difficult to seal them away with desiccants, is to concentrate on the more stable varieties. There are significant differences in stability with pyrites from different environments. The famous big cubes from Spain are relatively stable, as are the hydrothermal vein pyrites from the Huanzala mine in Peru.
jacques jedwab August 21, 2009 01:12PM
I was told years ago that soaking pyrite/marcasite pieces in hydroquinone helps fighting the decay. I have no details on dilutions, rinsing, drying, etc. An old trick, which I have not tried myself.
Mark J. Sigouin August 21, 2009 02:51PM
Pyrites aand Marcasites are subject to chemical weathering upon exposure to oxygen and water. The water can come from just the humidity of the air. Some pyrites are much more stable than others, but all, given time, oxygen, and water will decompose. The sulfide in the molecule become oxydized to sulfate as the oxygen combines with the sulfur.

Just as an aside, this it the basic reaction that occurs in the formation of acid mine drainage.
David Von Bargen August 21, 2009 04:29PM
Couple of good articles about pyrite disease.

Government recommendations:

Matrix can cause problems as source of water - re: halloysite

Under these conditions, relative humidity is unimportant: water for the reaction comes from a local source, and hydrous iron-aluminum sulfates act as “getters” for more water. Drying the materials worsens the problem by producing a dust that easily spreads to seed pyrite disease in other specimens. These seeds rapidly re-hydrate at higher humidity.
Albert Mura August 21, 2009 05:00PM
I can't add to the great comments that have been made here. As a pyrite collector for 30 years, however, I have found that once the pyrite oxidation has started its a self contained reaction and you are best to throw the specimen out, simple but sad.
Gord Howe August 21, 2009 07:23PM
I worked at the Sullivan Mine in Kimberley BC in the 70s and early 80s and have seen sulphide oxidation first hand. The mining procedure at the time was pillar mining where they would drill and blast a large volume of rock called a pillar then muck it out. The process left tons of sulphide based ore open to air where it would start oxidizing to the point where the rock would actually melt!. You can imagine the logistical problems this would cause with equipment, manpower etc. The main minerals were galena, sphalerite, pyrrhotite, and many other minor sulphides. Locally this phenomena is well documented and I'm pretty sure one of those old miners would be happy to share a "hot muck" story.

Anonymous User September 11, 2009 10:43AM

Please search for topic:

"Thiobacillus ferrooxidans" 2 years ago.There is an extended conversation about the same subject.Killing the bacteria and keeping dry won't help stopping the decomposition.

I'd like only to note here that the compounds required to stop the decomposition are very expensive!One should try only when talking about very important specimens.I have Pyrite from Madan only and I keep them in open air,I even clean the with acids and I wash them with water.They are so stable that even old pieces that had such treatment long before i handle them are still pristine and intact.It depends on many factors but the locality is very important!

All the best!
jervin goedhart October 24, 2009 11:26AM
I had a problem with my marcasites (I think they are, they are a little paler than Pyrite, these "bomb" shaped ones). I brushed them clean and then put thin transparent nail paint on them when I was about 16. They now are in open air for 20 years in a humid room with orgids and an aquarium as well. They are not to shiny to look fake, but, indeed, it is a cooping strategy with some negative esthastic result.

There is a tiny chance that all instable ones were lost anyway and I painted only the stable ones, it's 20 years ago....
Mary Jansson March 01, 2011 08:19PM
Hello There,
I found a rock ~ The rock is heavy for it's size ~ weighing 11.5 ounce's.... It measure's three and three quater's inche's long and is Two inche's wide.... The rock appear's to have quartz also a redish brown coating in some area's.... I wanted to see what was inside, so I took a little saw and tried sawing into it.... On the inside it is just full of bright and shiny silvery color of what I suspect is Pyrite.... Also has numerous cubicle's of golden color.... I did a streak test on rough tile and the streak is black on most ~ also golden on other area's ~ what kind of rock do you think it is and should I do anything to protect the pyrite? Doe's the mineral gold ever mix in with pyrite in a rock? It is a very unusual looking rock and very heavy for it's size....
Reiner Mielke March 01, 2011 09:31PM
I have marcasite specimens that are 40 years old that look as fresh as the day I found them. This is because I treated them. Other untreated pieces turned to dust in a few years. Here is how I treat them and I guarantee it will work on the most unstable pyrite or marcasite. First you wash all the oxidation off and soak the piece in water for a few days. Then you dry the specimen and submerge it in a water displacement protectant like WD40 for a day or two. Then you dry it and then submerge it in clean regular motor oil for a few days. After you take it out of the oil you set it in the sun on something absorbent and let the motor oil drain for a few days. The motor oil gets into the cracks and leaves a thin film on the surface that creates a reducing environment, end of problem.

Edited 2 time(s). Last edit at 03/02/2011 01:20AM by Reiner Mielke.
Jolyon & Katya Ralph March 01, 2011 09:37PM
Wow Reiner, you've solved a problem that mineralogists and palaeontologists have been unable to resolve for over a century.
Bob Southern March 01, 2011 10:58PM
Trust a Canadian to figure it out! :)-D

"If it can't be grown it's gotta be mined. "
Paul Brandes March 02, 2011 01:01AM
Not only does the WD-40/oil preserve your pyrite, it also keeps it from squeaking too...... >:D<
Jim Bean March 03, 2011 04:07AM
I'm sure the mineralogical world will be elated at the revelation of the cure to those pesky squeaking pyrites! :D
Jolyon & Katya Ralph March 03, 2011 10:53AM
I'm also delighted that Reiner "guarantees" it. Your pyrite safe or your money back!
Donald Vaughn March 03, 2011 05:05PM
calcium chloride in a small dish is a very good desiccant as well
Reiner Mielke March 03, 2011 09:31PM
If it starts decaying after the treatment I'll buy it off you, is that a good enough guarantee?
Or you can just scoff, not do the treatment and lose your specimen.

Edited 1 time(s). Last edit at 03/03/2011 09:42PM by Reiner Mielke.
Jolyon & Katya Ralph March 03, 2011 09:52PM
The main factors are environmental. I have a very low rate of pyrite mortality here in my flat, but the humidity is never particularly high, and obviously I am careful what I choose to keep.

But I have some samples that I fear for the future, so I'm going to test them with reiner's idea - I certainly can't see how it can do any harm, so I'm prepared to give it a try!

John Mason March 14, 2011 09:27PM

Something to consider too.

About 12 years ago I collected some amazing micros of reticulated pyrite from a mine in the Dolgellau Gold Belt - some of you may have seen a UKJMM note on them.

Some I hung onto, others went to a museum.

Where I lived at the time, 300m ASL in Wales and with hopeless heating, temperatures rarely went above 10C except for occasional heatwaves in the summer months - and then not far above! Humidity was often high, as one would expect in Wales. That is quite normal.

The museum was air conditioned and warm throughout all year round. The specimens I retained lasted just fine - the ones at the museum were dust within a couple of years. I figured temperature to be a major factor based on these simple empirical observations.

I think some varieties of pyrite will inevitably disintegrate quicker than others, but heat pushes the reaction along, based on these observations. Some others will clearly last a long time - I have Spanish and Peruvian pyrites >20 years in my collection that are the same visually as when purchased. Central Wales - my patch - produces some nice marcasite crystals at some localities, but frankly they are hardly worth collecting, as they "go woolly" withion 12 months and that's the first step to a heap of sulphurous powder that can knacker up even stable choice sulphide pieces from elsewhere!

Cheers - John
Anonymous User March 23, 2011 06:33AM

Please search for :

Thiobacilus Ferroxidans

in this forum.

David Zimmerman (2) August 27, 2011 12:47AM
I know, it's an old topic again and I'll probably get spanked, but decomposing Marcasite/ Pyrite are things I've cursed for years in the Upper Tri-State district of WI, IL, IA. My first serious attempt at stabilizing a piece came when I bought a killer piece from Bill Figi Sr. (before Barlow got there!) but it's penalty came with a 2" section that had 1/4" of sulfur powder on top of a marcasite area. The surrounding crystal areas were mat black sphalerite crystals. I used a wire brush and dental picks to remove all the loose sulfur, which exposed the marcasite. I then used a paint thinner to do some more scouring. Finally, the next week I used Rustoleum black mat paint!

While that technique sounds extreme, it has worked flawlessly for over 15 years on that piece and I doubt many of you would question the procedure if I was to produce before and after pictures.

Expanding off from that technique, and working with its success, I've since stabilized dozens of pieces of both pyrite and marcasite by first cleaning off any sulfur using abrasive measures. Then I put a thin coating of some light oil (WD40, mineral oil, or similar) on and bake it in the oven for at a low setting for 2 hours. Remove from oven and serve (:P). Joking aside, as soon as it is able to be handled (couple of hours later), I then spray the piece with an acrylic finishing spray that I buy at a craft supply supply store. It is used as a top-coat spray over artwork such as chalk and pencil to keep from smudging. I use a mat finish and can not comment on the gloss finish. I wait until it is dry and put a second and third spray coating on, depending upon the porosity of the material. Some pieces I have done as many as 5 coatings on.

This revised technique has worked well for me over the last 3 years and I have not seen any degradation of the pieces nor have I smelled any sulfur odors from them either. They are stored in a high-humidity area right inside my glass showcases for the world to see...not in some special containment area.

This is very similar to the other success story written above where the man used fingernail polish to seal it off. I find that the acrylic finishing spray is undetectable to my eye, and I'm sure it would pass the muster for 99% of the people reading this.

For Albert Mura above: Please PM me and I will be happy to pay for the shipping on all the pyrite that you are throwing away!! :D
Peter Haas August 27, 2011 01:45PM
<...> and humidity ranging from 5% to 75% <...>

I assume it is relative humidity you refer to. Now, if you had 75% relative humidity at -5 °C and 5% relative humdity at 45°C, this really wasn't much ...

Edited 1 time(s). Last edit at 08/27/2011 01:46PM by Peter Haas.
David Zimmerman (2) August 27, 2011 06:39PM

Some pyrite and marcasite pieces are from old locations and can not be replaced at any cost. I would value the price of the piece that I previously mentioned (the one I used Rustoleum on) well north of $1,000 and like I said, it just can not feasibly be replaced, unless someone wants to pump out 1,000 feet of mine water.

I have a hard time tossing or destroying material that took millions of years for nature to produce. I often consider myself the temporary caretaker for all of my minerals and try to preserve or clean them to the best of my abilities.
Anonymous User August 28, 2011 12:12AM
Hello and great posts:

Yes Peter I was talking about relative humidity and the maximum and minimum ranges my rocks have experienced during their travels across the Australian continent, and no not 75% at -5C, the values given were to show the wide ranges in both humidity and temperature my rocks have been exposed to and survived - including two cyclones. The causes of pyrite rot are complex for which there is no easy solution or answer. When I lived in Western Australia near the shores of the Indian Ocean, in fact just about 100m away from the shores I did a little test on a piece of fine grained pyrite I got from the Mt Isa Mines. I left it in the garden, in damp soil for over a year and it survived the test. I had a specimen of coarse grained galena which I collected during an underground trip to the Broken Hill Mines in 1997. It had a small quantity of associated pyrite and in less than a year the pyrite had completely decomposed to a white powder. Luckily the galena survived. Later I will be posting some photos of my pyrite disco balls from China. These balls had been kept in very damp conditions in a shed in China for well over a year, yet they show no signs of decomposition.

There was an article I read sometime ago about work done in a museum, the British Museum I think and the techniques and chemicals they used on decomposing "pyrite" fossils. They solved the problem I think but the procedure is not one you could easily do at home nor could you purchase the chemicals without some difficulty or expense.

And David I wish you all the best with your $1000 Pyrite specimen. Please post some pictures I would love to see it.
Ralph Bottrill August 28, 2011 01:17AM
Sam, unless you lived in the Snowy Mtns, knowing Australia I imagine that 75% humidity was at closer to 15-30C than -5C?
Pyrite disease is often related to inclusions and substrates of other minerals, especially marcasite, but possibly other metastable Fe-S-O minerals. These often form from the breakdown of pyrrhotite, which usually forms a lot of marcasite as well as pyrite and other minerals. I imagine that galena from Broken Hill would have been on pyrrhotite originally, but this mineral can be a lot more altered than it looks.

David Zimmerman (2) August 28, 2011 08:06PM

Here is a picture of the piece that I used black Rustoleum on to seal.

This again, was my first attempt 15 years ago when I was 18 at the time. I'm still very happy with the results, but maybe someday I will abrade the surface a bit to take the gloss off. You will notice a pile of sulfur in the showcase where a second piece of marcasite has left its tell-tail sign....someday maybe I'll get around to sealing that one as well, but the matrix on the piece is substantial enough for me not to worry about. The pen is for scale as well as pointing to the repaired area. What is strange about decomposing marcasites and pyrites are that the little marcasite flowers on the piece have not been sealed and appear to be stable. The only unstable crystals were attached to the matrix and not perched on the sphalerite xls. Largest dimension on the piece is 14.5" with a 3.25" galena perched next to the pen.

Here's a picture of pyrite balls perched on lepidodendron root that I found a few years ago.

I think the pyrite is not quite as shiny as I remember, but I could also be remembering the gloss on the other 100 I picked up and possibly this one never had was just too long ago. Either way, the pieces that I chose not to seal are just piles of dust right now and this one still sits in my showcase. Largest dimension is 7 inches.
open | download - Crystal Still Pictures 005.jpg (98.1 KB)
open | download - Crystal Still Pictures 006.jpg (104 KB)
Anonymous User September 01, 2011 07:11AM

Fixative spray and other coating will work on a specimen where decomposition hasn't started yet.

However,this hides the luster.

Also,temperature of the oven and oils can damage some Pyrite.

But,the most important note here is the interaction of the conservative methods with other specimens!Many recommended desiccants and this is correct-please read the post I recommended.

However,keep the desiccants away from hydrated species-I imagine there will be a problem.

I'd like to express my happiness when I realize how many people like Pyrite! I believe that it's the wide use of metals in our lives that makes many collectors call all metallic lustrous species "ugly black". First, someone who's seen a lot realizes that they do have color-there is obvious different between Galena and Tetrahedrite-and second I don't think they are ugly at all!I stop that here,but I couldn't resist expressing myslef!
Reiner Mielke October 12, 2011 09:48PM
Try my method, it does not affect the luster. First you wash all the oxidation off and soak the piece in water for a few days. Then you dry the specimen and submerge it in a water displacement protectant like WD40 for a day or two. Then you dry it and then submerge it in clean regular motor oil for a few days. After you take it out of the oil you set it in the sun on something absorbent and let the motor oil drain for a few days. The motor oil gets into the cracks and leaves a thin film on the surface that creates a reducing environment, end of problem.
Michael J. Bainbridge October 12, 2011 11:25PM
Why soak it in water for a few days? Seems rather counter intuitive.
Reiner Mielke October 12, 2011 11:57PM
Presumably some alteration has already taken place so the water will get rid of any iron sulphates and sulphuric acid cleaning the sample and allowing for better penetration of the oil into cracks and pores which were previously filled by the alteration products. For really serious alteration you may have to soak in HCl first ( to remove iron oxides) and then water (assuming there are no significant HCl soluble minerals associated with the pyrite). Maybe Iron-out would be better than HCl but I have no experience with it on Pyrite or Marcasite.
Anonymous User October 13, 2011 12:17AM
I do not wish to offend anyone so I am going to play the devil’s advocate here. You would not buy a car with significant structural rust nor a house overrun with termites so why invest in a “rotting” pyrite specimen. If it a museum sample or a rare fossil or even a gift that has significant sentimental value, maybe but an average sample of pyrite “kick –it-to-the-curb” and invest in a nice Peruvian piece or a Spanish beauty that is not rotting.
Michael J. Bainbridge October 13, 2011 12:24AM
That makes sense, thanks.

As for iron-out on pyrite and marcasite, I've not tried it yet either, but I'm told that it does a good job taking the dull tarnish off Nanisivik pieces. When I get up the guts to try it on mine I'll let you know.

Reiner Mielke October 13, 2011 11:31AM
Hello Samuel,

For the same reason people buy an antique car, because they don't make them anymore. Also this is not just about preserving old pyrites but preventing new ones from deteriorating. Think of it as rust proofing a new car.
Bart Cannon October 13, 2011 01:56PM
I have posted on this on Mindat within the last 6 months.

"Pyrite Disease" is caused by thiobacillus bacteria. They need some moisture to survive, as do all bacteria..

Apparently only an old timer such as myself knows that soaking an iron sulfide in a bacteriacide is the cure.

The product known as "Janitor in a Drum" worked well, but I don't know if it is still available.

There are surely other bacteriacides in the modern marketplace.

Nothing sadder to a mineral person than to see a beautiful pyrrhotite crystal cluster become 500 crumbs.

In the technical ore mineralogy literature there is a texture known as "chalcopyrite disease".

Not related to "pyrite disease". It is the un-mixing of copper in sphalerite and produces small blebs of chalcopyrite in sphalerite.
Michael J. Bainbridge October 13, 2011 02:19PM
If it's caused by bacteria, wouldn't just soaking it in alcohol do the trick? This should displace moisture, and kill the bacteria, no?
Jolyon & Katya Ralph October 13, 2011 02:56PM
Pyrite disease is NOT caused by bacteria.

If it were, it would be as easy as Bart suggests to cure. While, in some cases, bacteria may increase the speed of reaction, exposure to moist air can kill pyrite regardless of how it has been treated.

If you want to know the latest research about pyrite disease, ask a palentologist - they are much more concerned about pyrite decay than mineralogists are. Loss of a pyrite crystal is no big deal, but when your type specimen of an important fossil is pyritized, you really want to make sure it stays intact.

Bart Cannon October 13, 2011 03:04PM

Alcohol contains water and adsorbs additional moisture from the air. It then evaporates leaving the specimen moist and host to occupation by residual bacteria.

Bacteriacides linger and can function even if moisture is present.

I've never seen a true study on this, and only speak from notions of what I've heard elsewhere. I've never actually tried Janitor in a Drum.

I also have many ruined marcasites and pyrrhotites. Painful. I may seek out a modern bacteriacide and run a crude experiment.

The idea began with the problem of Tri-State marcasites disintegrating on their museum shelves and in the collection drawers.

Tri-State being the celebrated lead - zinc mines near Joplin, MO, Picher OK, and Kansas. I think there's a little bit or Arkansas in the district as well.

Peter Haas October 16, 2011 08:09AM

I do not wish to offend anyone so I am going to play the devil’s advocate here. You would not buy a car with significant structural rust nor a house overrun with termites so why invest in a “rotting” pyrite specimen.

There may be other minerals associated with the pyrite which are much more interesting. The classic galena after pyromorphite specimens from Wheal Hope, Cornwall, are often associated with pyrite that is particularly susceptible to decomposition. The same holds for many classic Wheal Jane ludlamites: they sit on pyrite.
Bart Cannon October 16, 2011 08:48AM

When it comes to bacteria and minerals, never say NOT. The bacteria don't cause the minerals to crumble, It is the byproducts of their metabolization that expand and disintegrate a specimen. They get their water for free from the air they drink and breath.

Every day we learn more about how pervasive bacteria are. 20 years ago we learned that stomach ulcers were not caused from stomach acid but rather the bacteria Heliobacter pylori.

Though I was challenged on this, I say automobile rust bubbles are caused by bacteria. Perhaps gray and brown rust primer paint doesn't seal against corrosion as much as its composition kills bacteria. Primer doesn't work unless the rust bubble is popped and scraped to eliminate the lovely, moist bacterial playground inside a rust bubble.

Anonymous User October 16, 2011 10:56AM

I think I said that too! Did you read my comment in full? We are not talking about that here, are we? Rather we are talking about someone’s rotting specimen. It is only my opinion but I would not risk “cross-contamination” or damage to my other beautiful pieces just to save some average looking rock that is falling apart. Sorry, but it is very easy and relatively inexpensive to get some real killer Peruvian or Spanish pieces I would not waste my time. I would leave the restoration work to the experts who are trained to do this type of restoration on samples of real scientific importance – archeologists/paleontologists/surgeons.
David Garske October 17, 2011 04:59AM
Many years ago Peter Embry mentioned that the British Museum used to treat their very best specimens with a bactericide (sp?) every 6 months to kill the bacteria. The bacteria convert sulfide to sulfate over a long time period.
Alfredo Petrov October 17, 2011 05:24AM
Dr. Fred Pough was another mineralogist who suggested, several decades ago, that rotting pyrite be treated with antibiotics.
Jolyon & Katya Ralph October 17, 2011 09:48AM
This thread is for the discussion of the causes and potential treatments for pyrite decay. If you want to discuss the merits/disadvantages of field collecting, or any other subject, then please do this in another thread.
Anonymous User October 17, 2011 02:15PM

I have to agree with Bart.To my knowledge,it's Thiobacilus ferroxidans that "eats" Sulfur and katabolizes Sulfuric acid.I'm not sure about the exact biochemical reaction,I couldn't find information on the bacteria,since it's not pathogenic,but without the bacteria there is no acid,so there is no decomposition.
Don Saathoff October 17, 2011 02:40PM
I haven't gone back and re-read this thread so someone else may have mentioned this in the past but, if you google "thiobacillus ferooxidans" Wikipedia has an informative article including information concerning it's use in "bioleaching" of sulfide ores.....

Jolyon & Katya Ralph October 17, 2011 03:43PM
The "pyrite disease is caused by bacteria" misnomer comes from the simplest of logical flaws.

"Some bacteria does eat (and can decompose) pyrite
therefore all pyrite decomposition is caused by bacteria, and treating your pyrite with a bacteriacide will protect it."

Unfortunately it's just wrong. Pyrite can decay with or without the presence of bacteria. While it's possible bacteria will accelerate the process, the real killer is relative humidity.

Keeping your pyrite dry is the only genuine way to protect it.
Peter Haas October 18, 2011 05:21AM
Also note that sulfide oxidation does not necessarily produce any acid. This is true for pyrite, but for many other sulfides, it's just plain wrong (note however, that many of these "other sulfides" readily decompose in humid conditions just as pyrite does). This will be evident from a look at the reactions (which should be considered in the first place anyway, when one tries to understand their implications):

Oxidation: S2- + 4 H2O -> SO42- + 8H+ + 8 e-
Reduction: O2 + 4 H+ + 4 e- -> 2 H2O

Thus, the oxidation of sulfide to sulfate produces as many protons as the reduction of oxygen consumes (sulfide -> sulfate requires two mols of oxygen). However, when oxidation starts from sulfur in a higher (more positive) oxidation state than sulfide (which is the case for pyrite and very few others that are composed of polysulfide anions), the reaction produces more protons than electrons and the solution turns acidic.

For all other sulfides, acid is only produced when metal ions (predominantly iron and manganese) precipitate as hydroxides, leaving protons behind, e.g. Fe3+ + 3 H2O -> Fe(OH)3 + 3 H+

Edited 3 time(s). Last edit at 10/18/2011 11:30AM by Peter Haas.
Bart Cannon October 18, 2011 07:57AM

If one could truly keep their iron sulfides ABSOLUTELY dry, then your opinion is correct.

But, of course, that is not possible, even in a partial vacuum.

There are splitters and clumpers in mineral classification, and a new dichotomy exists.

Bacteria believers and Bacteria deniers.

Some micro-biologist / mineralogist out there should do some cultures.

I have purchased some books on bacteria taxonomy, but there would be no reason for anyone to believe my findinds.

I have some pyrite liquors brewing, but the contamination factors will prevent any definitiave conclusions.

Jolyon & Katya Ralph October 18, 2011 08:54AM
Bart. You are right, it's impossible to keep pyrite truly dry.

So, perhaps all pyrite specimens are mortal and will eventually decay. But the dryer you keep them, the less chance they will turn to a powdery mess in your lifetime.

Of course, treat them with a bacteriacide, it will do no harm, but it is terribly harmful advice to tell people that this alone is enough to keep specimens safe.
Amir C. Akhavan October 18, 2011 10:40AM

In the case of pyrite and marcasite, isn't that

2S22- + 2 H2O + 7 O2 -> 4 SO42- + 4 H+

I might have missed something here...

Note S2- vs S22-

Edited 1 time(s). Last edit at 10/18/2011 10:41AM by Amir C. Akhavan.
Peter Haas October 18, 2011 11:19AM
You're right, but you also missed something. As I was saying in the introduction, the pyrite oxidation produces acid. I wanted to show, however, that the oxidation of many other sulfides does not.

EDIT: I have added a note to my previous post to make this a bit clearer (hopefully).

Edited 1 time(s). Last edit at 10/18/2011 11:21AM by Peter Haas.
D Mike Reinke October 18, 2011 04:29PM

This has been a great thread, I appreciate all sides, (and it has stayed civil....., so far!!) When I first got into minerals, I noticed in some old rip rap near my place, that most pyrite was dull but a few specks or even larger bits were very shiny still, having sat exposed for at least 20 if not 40 years. Of course, being a newbie, and ever optimistic, I thought maybe it was the trace content of gold that was so non-corroding, cha-ching! Later I read more on the subject, but this thread is even better. Thanks.

David Zimmerman (2) October 23, 2011 04:24AM
I've heard the bacteria theory years ago too, but I've never known anyone to successfully save the WI material using many kinds of bacterial killers. I've tried as have others I've known. Thanks to Riener on the last page for telling about the WD40 trick and process; I will be sure to try that when needed next time. I will also try to take before-and-after pictures to verify any luster loss on these processes.

Bart, I've got a lot of love for you but I agree with Jolyon that Bacteria can not be the sole cause for every case. This is evident in the picture I posted where the primary deposit is decomposing, yet the secondary flowers are stable. In the sealed area the two types of marcasite are touching each other.

On a related note: I was digging in an old WI tailings pile a few years ago and was seeing typical iron rusty blebs (completely decomposed marcasite xls) on the pile material but was shocked to find material that looked fresh-as-the-day-it-was-mined only 3 feet under the surface of the pile. I was shocked! ::o

I'd love an explanation from the pyrite gods on that one. Over 100 years of rain, moisture, and plenty of opportunity for the bacterial culture to create it's pile of paradise, and yet perfect crystals only 6 inches away from decomposing ones.
Nicu Pascanu October 23, 2011 10:25AM
OK, in physico-chemical study, all those listed here are well-known themes. But if two or three years after collection then, and if it took place in adverse environmental conditions (high humidity), you find that begin to decay, it is required to do any test, empirically whether and try to solve the problem. Several years ago I did some tests by funny idea. I treated pyrite, marcasite and some Fe-sulphides pseudomorphs, about 5 samples, found in a advanced disease condition. I used Meroterpene compound. As long as it don't know, absolutely, all the factors to initiate that decomposition, this approach is certainly empirically. The result is however encouraging, 3-4 years ago these samples seem to be stable both inside and superficial, too. They are kept in "quarantine" now.
I wouldn't want to be misunderstood here, this is just a test that could have only positive response in some specific conditions.

Cheers, :)
Matt Zukowski September 09, 2012 02:34AM

It could be that the reason that the pyrites and other sulfides are fresh only three feet below the surface is that there is too little oxygen at that depth. Redox gradients can be quite steep with slow movement of water in a porous media. In this case, although the water falling on the site is oxygenated, as it infiltrates it quickly becomes oxygen depleted, so the oxidizing environment extends only a short distance into the subsurface.
Bart Cannon September 09, 2012 12:49PM
I must sheepishly admit that I've never actually employed the bacteriacide approach to saving marcasite and pyrrhotite. I've never thought that pure pyrite would need any treatment.

The age old bacteriacide for saving marcasite was Janitor in a Drum. It has long since lost its retail neighborhood oulets. It is still available from a single central supplier, but only in large volumes.

The reaction pathways in the weathering of sulfides is incredibly complex. An almost endless series of intermediate and transitional phases..

There is an excellent book on this subject.

"Oxide Zone Geochemistry" P.A. Williams, 1990. Ellis Horwood Publishers.

I'm still curious about the process which produces museum drawer acanthite fuzz.

John Oostenryk April 23, 2013 06:45PM
re: specimen saving- and my reply following Tim Jokela's post on the separate thread regarding pyrite beads...
I figured I would chime in here- since this is where Reiner's methodology was first posted.

As many other posters reacted at that time, I also was amused/disgusted when I read Reinier's proposed method with oiling. I thought, "Good God- what a mess! The guy must be crazy!"

BUT- after realizing a local connection between oil/bitumin pockets associated with long exposed and completely intact marcasite crystals... and therefore, some later, related reflection...
I resolved to engage in an ongoing product test with various control groups to account for none/some state of decay prior and variety of inside/outside environment factors.
I couldn't bring myself to do the glooping oil factor, but did use full immersion in WD-40...
So, the reveal?

Earlyyyy results are- at an ~year and a half and continuing, nooothing is changing on my marcasite/pyrite pcs... So good news so far...

...I intend a report of my results with details and pics for Mindat- it is pending- no hurry...
Thought it would be good to get that positive data out sooner for my fellow mineral collectors, who hate the sad scene of trashed minerals and despise the smell of decomposing Marcasite!
(There is some putting up with the WD-40 during processing, but that is what garages are for:)


ps: Jolyon- what do you see in your project version so far?

Edited 2 time(s). Last edit at 04/23/2013 10:50PM by John Oostenryk.
Tim Jokela Jr April 23, 2013 07:14PM

Rest assured that Reiner is far, far from an idiot, and his method makes sense. Bacteria or chemical reaction, it deals with both.

He's a 4 decade fanatical field collector / prospector / geologist / miner, ingenious at mineral ID and prep, and is not short on brains.

NO gloop is involved in the Mielke Method! The oil I used on my old rotten pyrite drained off fully... it's not at all what you'd think. The piece looks perfectly clean and there's only an odor if you put your nose right up to it.

I'm kicking myself for not having the balls to similarly treat a 3" pyrite pseudo after pyrrhotite, which turned to $175 worth of dust.

To all in doubt, try it out!

It's cheap, and easy...

just like the girls I like.
John Oostenryk April 23, 2013 09:28PM
Hi Tim,
I changed my wording to better relay the minor content of my post, it seemed to impinge a bit, and I fully did NOT intend that interpretation...
BUT, oh yes- shocking? of course! Same as if someone said dip them in syrup! Gnarly-lol!
I actually do suspect the oil cuts the WD-40 vapors too?! So shoulda went all the way with some... I'll try that too yet, no doubt~

The major point was, as you know, to relate that THIS IS, very successful so far. Two positive reviews at one time are louder than single statements here and there!
I felt it best to get that news out to folks now, as I have been waiting quite a while. Some science is slowwww-LOL. Patience IS a virtue.

I thoroughly relish a 'successful pretreatment process' to avoid that stinking nasty odor of decomposition!!!
I have done some serious cleanup in other venues of old specimens which had formed huge piles of friable 'dust'. Gack- it was so horrible!

Anyhoo, gotta fly, but I had to rectify that misunderstanding for Maggie, she is always so pleasant, I was truly bummed to see her wroth:(
Maggie Wilson April 23, 2013 09:59PM
Yeah, I knew I should have counted to ten... or maybe ten thousand... upon reading and re-re-re-reading, I can see that you meant no ill will.

I'm better now. Thanks, John, for your remarks.

John Oostenryk April 23, 2013 10:57PM
HI Maggie,
I'm glad you brought it to my attention- I should have waited till I had more time to post a better rendition of what I was trying to convey...
...Figures- I spent 4 times as much time trying to sort it out~ack!
Thanks for the understanding:)
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