[NHCOLL-L:2987] Re: Coal Ball Storage to Prevent Pyrite Decay

[csturmjr+ at pitt.edu]

> As I am re-housing the coal balls that we have in our collection I have
> discovered that the microcrystalline pyrite or chalcopyrite in some
> specimens has oxidized creating the characteristic white powder and acidic
> odor of pyrite decay/"pyrite disease."  Therefore, I am currently
> investigating how to store the coal balls that we have in our collection
> to: 1) slow down this process, 2) prevent those that have not begun to
> oxidize from doing so, and 3) keep them from affecting the rest of the
> collection that are not coal balls and are not affected.

I offer the following information from a chapter that I have in press:

"You might have the occasion to collect fossils that are composed of
Pyrite. Pyrite will start degrading at elevated humidity and give off
acidic gases. This condition is call Pyrite Disease (or more recently
Marcasite Disease), though as in the above discussion on Bynesian Decay,
it is not a bacterial disease. I prefer the term Pyrite Decay (Marcasite
Disease has not yet gained widespread use). In Pyrite Decay, iron sulfide
combines with oxygen and water and forms iron sulfates and sulfuric acid.
The result is that the integrity of the specimens is destroyed. If any
calcium carbonate shells are present, the sulfuric acid can precipitate
Bynesian Decay.

Many techniques have been proposed for preventing Pyrite Decay. Their
basis is to prevent the specimen from coming in contact with air either by
encasing the specimen with an artificial resin or submerging it in a
liquid such as glycerin, paraffin oil, kerosene, or silicone oil. None of
these techniques work well.

The best prevention is to maintain the pyrite specimens in a low relative
humidity, around 40-45%. If some degradation has already occurred,
neutralization of the degradation products with ethanolamine
thioglycollate may help (Cornish and Doyle 1984). Some researchers
advocate placing specimens in an oxygen free environment (anoxic
environment). This technique is beyond the scope of this chapter but you
can read about it in Burke (1996).


Burke, J. 1996. Anoxic microenvironments: a simple guide. SPNHC Leaflets
1(1): 1-4 (Spring, 1996). [SPNHC is the acronym for the Society for the
Preservation of Natural History Collections].
Cornish, L and A. Doyle. 1984. Use of ethanolamine thioglycollate in the
conservation of pyritzed fossils. Paleontology 27: 421-424.

Regards,
Charlie
.................................................
Research Associate - Section of Mollusks
Carnegie Museum of Natural History
Pittsburgh, PA, USA

Assistant Professor - Family Medicine