[NHCOLL-L:394] Re: pyrite disease?

[Sally Shelton]

One of the first indications that you have pyrite oxidation ("disease" is
pretty much a misnomer) is knowing that you have some kind of FeSOx
compounds in the parent rock/matrix. If you don't, you don't have pyrite
oxidation. If you're wondering, you can do X-ray diffraction of a small
representative sample just to see what compounds are present. 

Trick 2: Scrape off (carefully, without crushing) a sample of the growth
and look at it under a dissecting microscope. Salt crystals and mold
structures look wildly different under any magnification. Pyrite oxidation
breakdown products don't have much real structure. If it looks like a mold
growth, you can skip the XRD work. If it looks crystalline, you may
(especially given your location) indeed have salts efflorescing. 

In all 3 cases, a low and controlled RH will help. So you could take
samples now, put the specimen in a controlled-RH environment, and then take
some time to figure out exactly what you've got. 

At that point, write back to this list--it's no good going through
everything you might do in any eventuality. 

Cheers,
Sally Shelton
Collections Officer
National Museum of Natural History
Smithsonian Institution