[NHCOLL-L:5512] RE: marcasite disease

[Shelton, Sally Y.]

There is a lot of misinformation on this subject. As often happens, it comes down to factors in the storage environment vs. the inherent vice of the specimen. 

Pyrite breakdown and marcasite breakdown are the same thing, first of all, because they are polymorphs of the same compound. Both are susceptible to oxidative reactions which cause irreversible breakdown and the liberation of acidic byproducts (specifically sulphuric acid). This can be accelerated in high-humidity situations. Obviously, not all specimens break down. The smaller the grain size (as in marcasite and framboidal pyrite), the larger the total surface area, and the more likely the specimen is to be susceptible to this breakdown. The best preventative measure is to have the specimens in a fairly dry environment (~40% RH) , and I would avoid acid-emitting materials such as wood and some paper/cardboard products as well. Specimens that have begin to deteriorate should be moved to a very dry environment (~30% RH) for stabilization. For important specimens, you may want to look at some kind of anoxic storage, but the RH should be closely monitored with that system. There are some complex treatments for deteriorating specimens, but they are not recommended for every situation. 

Here are some references: 
http://collections.paleo.amnh.org/6/storage-environments 
http://www.nps.gov/history/museum/publications/MHI/AppendixU.pdf
http://www.vertpaleo.org/AM/documents/Shinya_and_Bergwall_2007.pdf

It's not a disease as such and it is not "contagious" from specimen to specimen. Specimens with similar chemical and structuiral characteristics may react similarly to adverse environmental conditions, and specimens in the proximity of  a badly-deteriorated specimen liberating sulphuric acid may show adverse effects from the acid contact. 

I would remove a deteriorating specimen from its current storage environment for its own sake, and find out what exactly was happening in there. The solution may be as simple as lowering the RH or as complex as rebuilding the storage system. But marcasite does not "infect" pyrite; you are quite correct on that point. 

Sally Y. Shelton, Interim Director
Museum of Geology and Paleontology Research Laboratory
South Dakota School of Mines and Technology
501 E. St. Joseph
Rapid City, SD   57701
phone 605.394.2487
email Sally.Shelton at sdsmt.edu
________________________________________
From: owner-nhcoll-l at lists.yale.edu [owner-nhcoll-l at lists.yale.edu] On Behalf Of Bob Glotzhober [bglotzhober at ohiohistory.org]
Sent: Wednesday, June 15, 2011 6:54 AM
To: NH Collection List Server
Cc: Brad Lepper; Jason Crabill
Subject: [NHCOLL-L:5511] marcasite disease

I need some help understanding better what has been called “Marcasite Disease.”  As curator of all our relatively small natural history collections (circa 29,000 cataloged items) within our state historical society museum, I deal with all types of natural history collections – and minerals are one area that is not within my expertise nor training. (But I keep on trying to learn!)

I recently had a visit by a couple of mineral collectors – who seem very knowledgeable. They noticed in our exhibits that we have a nice specimen of marcasite adjacent to a nice pyrite. It seemed logical as they are related types. They said that having these in close proximity would cause marcasite disease – eventually destroying the pyrite. This concerned me, as specimens of both not on exhibit are also stored in the same collections cabinet. Therefore, many specimens are within the same cabinet, although on different shelves. I talked with a more mineralogically knowledgeable friend, and he said he thought (though not certain) that “marcasite disease” (not really a disease) affected mostly marcasite and was now thought to be primarily a humidity problem.

Which of the above is correct – or are both somewhat correct? Do I need to move my exhibit specimens to separate them, and if so – how far apart? Do I need to re-shelf our collections so these are in different cabinets? Or am I AOK?

Bob Glotzhober

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Robert C. Glotzhober                           e-Mail:  bglotzhober at ohiohistory.org<mailto:bglotzhober at ohiohistory.org>

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