Learning Center What is a mineral?The most common minerals on earth Information for Educators Mindat Articles The Elements The Rock H. Currier Digital Library Geologic Time

Minerals by Properties Minerals by Chemistry Advanced Locality Search Random Mineral Random Locality Search by minID Localities Near Me Search Articles Search Glossary More Search Options

The Mindat Manual Add a New Photo Rate Photos Locality Edit Report Coordinate Completion Report Add Glossary Item

Mining Companies Statistics Users Mineral Museums Clubs & Organizations Mineral Shows & Events The Mindat Directory Device Settings The Mineral Quiz

Photo Search Photo Galleries Search by Color New Photos Today New Photos Yesterday Members' Photo Galleries Past Photo of the Day Gallery Photography

Discussions

💬 Home 🔎 Search 📅 Latest

╳Discussions

💬 Home 🔎 Search 📅 Latest

Groups

Recent Images in Discussions

Techniques for CollectorsMarcasite

6th Sep 2002 10:56 UTClittlebigfoot

Hi

We recently went to France and there i have found a huge marcasite ( very beautiful by the way), but now comes my question: Some books say that you shoold keep Markasite in a closed sac or box to prevent oxidating in the air, others say its only the close related Pyrite that shows this uncommon thing. i don't know wich one to believe, so how can i keep my markasite clean ( no oxidation..)

Thanx

yours sincerely

6th Sep 2002 11:06 UTCJolyon

Both marcasite and pyrite will decay in damp air.

You must keep them dry (low humidity) to prevent this. Keeping in a box with some dessicating agent, such as silica gel, will help.

Jolyon

6th Sep 2002 16:28 UTCAlan Plante

Hi again!

Both marcasite and pyrite are subject to what is known somewhat tongue-and-cheek as "pyrite disease." Not all specimens of either are prone to this oxidation decay, but far more marcasite seems to be than does pyrite.

Quite frankly, I don't think anyone has come up with a sure-fire way to prevent the problem - and I'm afraid keeping them in closed bags or boxes isn't a solution either. Leastwise not one of those steps alone.

The problem is moisture. Moisture in the air - humidity - tends to be slightly acidic. And it is that acid which slowly reacts with the minerals, decaying them. So the best solutions to the problem are those that involve sealing the specimens in dry containers, and keeping them dry. The specimens must also be thoroughly dried before being placed in the containers. If either the air in the container or the specimen have any moisture, the decay will occur.

The best method I've heard of is to: 1) Dry the sample by heating it gently in an oven set at its lowest temperature, for at least an hour or two, then 2) place the sample in a plastic box with a clear cover (such as a "Perky" box), along with a small packet of dessicant, and 3) seal the box with a non-acid tub-and-tile caulk that remains elastic (place a 1/8" bead of this around the edge the top seats on, then press the top down into the sealing material.) The dessicant wicks away any moisture in the air in the box, and the sample stays dry in the sealed container. If you can, place the boxes, open, on a sunny porch on a warm to hot day when it isn't too humid. That environment is about the driest you can manage for working in. You'll cut down on the amount of moisture that gets sealed in the boxes with the air you seal in.

That still isn't sure-fire - seals tend to dry out and crack over time - but it's about the best I've heard of, short of having the samples hermetically sealed in a vacumm... :~}

This problem is more prevalent in ares with a humid climate - people who live in arid regions have better luck keeping marcasite and pyrite specimens.

Good Luck!

Al Plante

PS: Whatever you do, DO NOT wrap pyrite or marcasite specimens in newspaper!!! Newspaper-wrapped samples decay the fastest. - The sulfur in the paper reacts with humidity to form sulfuric acid, so you are essentially wrapping the pieces in an acid-generating medium...

6th Sep 2002 16:29 UTCAlan Plante

Hi Jolyon

I guess we were both typing replies at the same time - and you hit "Submit" first!

:~}

Alan

6th Sep 2002 21:48 UTCRob Woodside

Bart Cannon swears by soaking the marcasite in "Janitor in a Drum" for a day or so before rinsing. He claims that marcasites will then survive Seattle climate, however I think Al is right.

8th Sep 2002 07:05 UTCEvan

Hi,

in addition to the steps Alan mentioned, it may also pay to wear gloves while handling the specimens - skin oils contain a certain amount of acid. I read an article on preserving pyrites at one stage (I'll see if I can find it) which said that once a specimen had started to decay, it was almost impossible to stop it, but that if you can prevent it from starting and store it in a low-humidity environment, it should last OK.

Regards,

Evan

9th Sep 2002 02:53 UTCAlfredo Petrov

I'm more pessimistic than our colleagues here - No matter how dry you keep it, or how much acid you try to neutralize with NaOH or whatever, your marcasites will still decompose, perhaps a little more slowly, but they are nevertheless doomed. Minuscule traces of water vapor, such as just one breath breathed on the specimen while looking at it are quite sufficient for the reaction to continue. The mineral recycles the minute traces of water present, forming hydrous Fe sulfates which eventually turn into FeO(OH) and give up some of their water to continue the reaction on the FeS2 molecules next door.

A few lucky collectors have access to marcasite localities that somehow seem less susceptible to desintegration. Vintirov in the Czech Republic is such a lucky locality. (Rob, do you happen to know why this might be?)

Now I'll write something quite heretical, but it seems to work for me: Instead of trying to neutralize the acid, or dry it up, which are both impossible in the long run, I soak my pyrites and marcasites in strong HCl, then rinse BRIEFLY in water to get excess acid off the surface, and let it dry. They stay brightly metallic and unaltered for many years (well, 6 years so far). Call it "mineralogical judo". Whether the treatment is permanent or not I can't say yet. I'll report back in another 6 years.

Greetings from Alfredo

13th Sep 2002 20:24 UTCRob Woodside

I have a wonderful fiveling of bright marcasite from Vintirov. It is nearing its first decade in my possesion and I'm delighted to hear that this is one of the less suseptible localities. In the 60's Ernst Windisch swore up and down that a lovely Treece cockscomb Marcasite would last forever, so I paid $2.50 for it. Sadly it lasted only 25 years, about 15 more than poor Ernst. When they start to go, they go fast and it seems to be in the nooks and crannies of the specimen that the rot takes hold. The pyrite Suns from Sparta are sometimes marcasite or the intergrowth "melnikovite" and these are quite unstable. I have a pure pyrite sun with a lable from the 1800's that is in perfect shape. The type locality Argyrodites are getting smaller. The Saxony Argyrodites are on rotting Marcasite! Many Butte specimens with pyrite suffer as well. The Redpath Museum at McGill in Montreal had a systematic collection laid out on cotton batten in the early 1900's and had probably sat untouched for over thirty years by the time I saw it in the 60's. The fragments and acid eaten cotten told the tale, with some localities more suseptible than others.

George Robinson stores marcasites in water, apparently to good effect. He argues that they live for millions of years in mine waters anyway.

The fact that a specimen will last for decades and then within a few months fall apart, leaving single xls intact, but with a limonite? (or iron sulfate? it looks like limonite) coating where they were attached; suggests bacterial action to me. Thus any resistant locality would be explained as producing specimens that were somehow inhospitable to the bacteria. Notice that all the methods of preservation suggested: disinfect the specimen, hermetically seal it, or deprive it of life giving water, all make it difficult for bacteria. What is needed is a Pasteur experiment to show that pyrite disease is not spontaneously generated.

17th Sep 2002 12:46 UTCAlfredo Petrov

I think Dr. Fred Pough was the first person to suggest that antibiotics might stop marcasite rot. I like George Robinson's idea of storing them in water - If nothing else, it at least protects the labels, boxes and other specimens around it. This water idea might work because the water rapidly becomes acidic and, as I mentioned in a previous post, I think most collectors are doing their marcasites a disservice by trying various techniques to neutralize the acid - better to acidify them more. I'd rather store my marcasites in sealed jars of fairly strong acid (not of course HNO3).

1st Nov 2014 16:33 UTCLisa Kinder

Hello Alfredo,

I read your post today, Nov. 1, 2014... just curious how your marcasite has held up over the last twelve years. I purchased a palm-sized cockscomb at an estate sale, about a month ago, and it seems to be developing more "rust" than it had before. I live in Colorado, which has relatively low humidity (30-50% -- relative to tropical climates.)) I see that you soaked yours in a strong HCl solution...when you say, "strong", do you mean 100% or more like 80/20? How long did you soak it?

Thanks for your help!

Lisa

1st Nov 2014 17:39 UTCReiner Mielke Expert

Lisa have a look at this thread: http://www.mindat.org/forum.php?read,19,149266,215818#msg-215818

1st Nov 2014 19:00 UTClittlebigfoot

-- moved topic --

1st Nov 2014 22:07 UTCLisa Kinder

Thanks, Reiner! Very interesting; I read the entire thread... not sure if I should go with the oil method or sealant method. I'm leaning toward the oil method. Although messy, it makes sense that the oil would probably penetrate into the tiny cervices more efficiently and "smother" any type of chemical or bacterial reaction occurring in the marcasite. I hope I don't ruin it, but it sounds like it may be doomed sooner or later so why not postpone it if I can.

1st Nov 2014 23:05 UTCDavid Garske

The problem is a "bug" called ferrobacillus which oxidizes iron, and it really likes iron in pyrite and marcasite. Peter Embrey from the British Museum told me many years ago the the museum dipped their best specimens in a antibacterial solution every 6 months. Look it up on the net, a lot of information is available.

Dave

2nd Nov 2014 13:48 UTCReiner Mielke Expert

I guess you can dip it in antibacterial solution every 6 months. But to me dipping it in motor oil once is much easier.

19th Apr 2015 15:45 UTCPaul Stephen Cyr

From the advice of a little boy on the net, I have halted advanced "pyrite disease" on a marcasite on calcite piece by soaking it in WD-40 (household lubricant) for a few days. This piece has been stable for over a year now. I recently acquired a great cockscomb marcasite from Czech Republic, and have not tried anything on that. Supposedly that material is quite stable.

19th Apr 2015 16:04 UTCStephen Rose Expert

Paul,

I have had a nice marcasite from the Czech Republic for about 40 years with no noticeable change to its' brightness. No special treatment required.

Cheers,

Steve

19th Apr 2015 16:14 UTCPaul Stephen Cyr

(tu):-D

Mindat.org is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization.
Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: April 26, 2024 21:15:25

Go to top of page