[NHCOLL-L:2988] Re: Coal Ball Storage to Prevent Pyrite Decay

[Joy Irving]

I have some experience of prevention of pyrite decay in minerals and 
palaeontological material.  It is generally recommended (and I know from 
experience) that storage of pyritic material should be at or below 30% RH 
unless all oxygen can be excluded.  This should be done by means of 
conditioned silica gel in micro-environments (polyethylene boxes), which is 
relatively inexpensive, or the use of oxygen-free mico-environments with 
barrier film and oxygen scavengers (a little more expensive!).

In addition to the papers already recommended below, I would add : Waller, 
R.  1987.  An Experimental Ammonia Gas Treatment Method for Oxidized Pyrite 
Specimens.  Preprints (Working Group 13), pp. 623-630.  ICOM Committee for 
Conservation.  8th Triennial Meeting, Sydney, Australia, 6-11 September, 
1987.  Getty Conservation Institute, Los Angeles.

Also : Howie, F.M.P.  1992.  'Pyrite and Marcasite.'  In 'The Care and 
Conservation of Geological Material'.  Howie, F.M.P. (ed.).  London : 
Butterworth-Heinemann.  pp. 70-84.

Joy Irving.
Oxford University Museum of Natural History.



>From: csturmjr+ at pitt.edu
>Reply-To: csturmjr+ at pitt.edu
>To: paleocatstar at ou.edu
>CC: NHCOLL-L at lists.yale.edu
>Subject: [NHCOLL-L:2987] Re: Coal Ball Storage to Prevent Pyrite Decay
>Date: Mon, 06 Mar 2006 23:25:57 -0500 (EST)
>
>
> > 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
>