FMF - Friends of Minerals Forum, discussion and message board

[Tracy]

In the 7 years that I have been living in my current home, I have had 2 pyrite "sun dollars" from Illinois become dull and brittle, and eventually crack or break into pieces. I just acquired a third sun dollar and would like to know what is causing this so that I can prevent it from happening again. I presume it is somehow related to humidity because my home can be very humid (90-100%) during the summer and then very dry during the winter. The temperature does not fluctuate as dramatically as the humidity inside the house, though I do not have any climate control system. Can you advise me on why this happens, how to protect my newest sun dollar, and whether I should be concerned for other pyrite specimens in my collection as well? Thank you.

[Jordi Fabre]

TAK,

Some minerals as for example many Marcasites, some Pyrites, Realgars, several highly hydrated minerals...are sensitive to the humidity. No too much chances to save them excepting creating an special microclimate on your home where the minerals stay with down and stable humidity rate. Of course it is quasi impossible to do it in a regular home where common people leave.
Plus some of these "sun dollars" was acidified to increase (temporary) its beauty becoming more shinny. Unfortunately, the esthetics results is no so good for the "sun dollar's" healthy as its decay starts still faster due the remaining traces of acid, badly eliminated.

I suggest to you to do the next: go the a main drug store, buy an amount of the more pure alcohol (without water on it) that you can find, put it on a bowl, merge the Pyrite inside, leave it there for a while (5 minutes for example) and then take it off and try to dry completely the "sun dollar" helping with a regular hair dryer.
After that, and using a colorless and no brilliant hair's gum-lac try to cover completely the whole "sun dollar". When it becomes dry again, voilà! you have it more preserved.
I suggest to you to try it first with some old damaged "sun dollar" to prevent some unexpected bad results on the new one.

Hopefully it helps.

Jordi

[Carles Curto]

TAK from NJ wrote:
Not only “Sun dollars”, most of the pyrite nodules use to be problematic because its interior is crystallized not on fresh Pyrite but on Marcasite, which is much more unstable. The growing process of chemical degradation of Marcasite is not visible to us because the exterior core of Pyrite hides the processes that it can be quick or slow depending of each case. For example on the Museum of Barcelona we conserved a very nice nodule, a floater, from Bohemia. The nodule registered on 1916, was absolutely bright and clean, and it was exhibited on sulfide cases. Last revision (our protocols of preventive conservation stablished a weekly general revision of exhibited specimens and a continuous revision of the general collection) didn’t reveal any change or struggle. One morning of 1984, the security agent heard a sound on the exhibition room. The Czech Pyrite was on its case, absolutely fragmented and conserving the bright core but now yes, showing an inner melange of bad-smelling powder and hair of ex Marcasite.

Then if you add some nodules (also the new Macasite specimens) you must think they use to have a limited life. To prevent the alterations and enlarge the life of the specimen you can do:

Never clean Marcasite, Pyrite, Arsenopyrite and similar sulfides with current water, or acidulated water, but if you do it a latter immersion on alcohol is necessary to eliminate any rest of water on the sample.
If degradation is not very advanced you can intent to wash the specimen on alcohol and immerge it before on powder of sodic bicarbonate, but that can only give a longer life (not so long) to the specimen.
Be careful wen you acquire new samples to the matrix. A matrix rich on Marcasite is a potential danger for the entire specimen.