[NHCOLL-L:2984] Coal Ball Storage to Prevent Pyrite Decay

[paleocatstar at ou.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 have done some research/reading on pyrite decay in specimens.  From that, I have determined the recommendations are to prevent it in the first place by keeping them at a low and constant relative humidity.  We have a relatively controlled collection storage environment with the goal of a constant humidity of 45% and 68°F temperature.  However, some specimens already had pyrite decay before we controlled the humidity and temperature.  There is some indication that limiting their exposure to oxygen in the air might slow and/or prevent the decay since is an oxidation process.  However, we do not want to coat the coal balls with anything because we would lose the ability to work with them in the future.

I have heard from one individual that perhaps putting some activated charcoal in the same Steel Fixtures Cabinet would help control any build up of acidic gases that may arise.

I was hoping someone knows of additional publications about or has some personal experience with pyrite decay, especially with coal balls or other paleobotanical materials that might be helpful.  It would be useful knowing what did not work as well as what did or might work.  Any help would be appreciated.