FMF - Friends of Minerals Forum, discussion and message board

[robhanson]

Hi All,

Thought I'd post here and see if I can get some advice! We fossil on and off in England and have some nice fools gold ammonites. I've cleaned them in coke and then pure water (store bought as our water in Salisbury is very hard) and then stored them. I just took them out about 5 months later and have found crystals growing on a couple of them. I rinsed them off with hard water and a few days later they've started to grow again. I'm worried that this will start to break down the fools gold so plan on lacquering them (or otherwise) to prevent it. Is this a wise idea, or is there something else people would recommend?

I've attached photos of the crystals starting to regrow (small white substance on the ammonites).

Thanks,
Rob

[alfredo]

The white whiskers are iron sulphates produced by oxidation of the pyrite ("fools gold"), so yes, the pyrite is rotting and will fall apart. Best keep them in a dessicator to slow down this process - as dry an atmosphere as possible.

Lacquer doesn't work very well, especially not if there are even the tiniest traces of moisture remaining in submicroscopic pores in the pyrite (which there probably will be). The lacquer just holds in the invisible traces of moisture and lets it continue doing its evil deeds.

Museums have a better process for preserving pyrite (vacuum pumps and lacquer), but it isn't worth the trouble except for the most valuable specimens. Best just focus on keeping it in very dry air. If you live in a swamp, you'll need a desiccator.

[robhanson]

Thanks for the great answer, very useful. It seems sad that something we took from the sea/beach that has lasted for millions of years can break down so quickly once its removed. I think we'll put them back in sea/salt water until we can figure out what to do with them.

Thanks again for the answer,
Rob

[Pete Richards]

[Rei]

Every guide I've seen on pyrite stresses the same thing: dry, dry, dry. There's all sorts of various things you can do, but the one thing that matters more than anything else is keeping all water, even humidity, away.

[robhanson]

Thank you all for the great replies. England's about the wettest country there is it seems, I think I'll take them to a lab at work where have hot rooms/ovens to dry them out and then put them in a sealed frame, finders crossed that'll keep them safe.

It's strange as we've had some at my parents house for years which haven't had this happen, and its not all of our ones that have had it. I did notice that the oxidation mainly seems to occur on gaps where there isn't fools gold present, so I guess the water is more heavily adsorbed by the rock under the pyrite which wasn't fully dry.

[Don Lum]

[alfredo]

Don, I don't think you need any special treatment for anhydrite. It slowly hydrates to gypsum, in Nature outdoors, over long time periods. But indoors in a collection it should be fine, even in your humid summers.

Halite will depend on what impurities might be present. Pure halite is a remarkably stable mineral; it doesn't absorb moisture. Unfortunately there are often other species (magnesium-bearing salts) present which do absorb moisture from damp air, so any need for desiccation will depend on whether your halites have those other minerals present or not.

[Don Lum]

[Don Lum]

Hello Rob,

There is one other thing I would like to mention to you but this may not be the solution to your problem if there is much water still in the ammonite and there probably is. You have mentioned sealing it and Alfredo responded about any water left in the specimen. When I extracted a marcasite specimen from a wall in Hot Spring County a number of years ago, the local Rock Club guide, Jimmy Matlock, told me to mix White Elmer's Glue with water in equal amounts and paint the specimen with the solution. I have posted that specimen on FMF under Marcasite Weenie Dog. You can see the white glue in the pictures where I left too much glue on. It has not crumbled to pieces and disintegrated like a lot of specimens I have seen but it has developed a crack. Dr. Peter Megaw wrote a post on FMF with the same technique for stabilizing the crumbly gossan or limonite matix on which specimens like adamite from Mexico are found.

If you can dessicate your specimen and then coated it with the white Elmer's Glue that might help.

Regards,

Don

[Rei]

You can buy silica gel packets in bulk online. I've never tried resetting them in a conventional oven. I've done it in a microwave, but it's tricky. You to get the power just right so that they dehydrate but don't melt. And reset packets don't seem to last as long.

It'd be best if you can get a perfect seal so that you never have to switch packets, but that's really hard to do. If you tire of changing individual packets, you can get a bulk solution, like those buckets of deliquescent salt that you just have to empty the water when it gets too high - those are used to keep whole storage units dry for months at a time. If all that is too complex, I'd just go for a really good initial dehydration and then try to store it in as naturally "drying" of a location as possible, such as near a vent register or a place in the house that's warmer than others.

@Don: Why white elmers glue? Why not clear polyurethane? I mean, that's actually designed to be a transparent sealing coat (whether paint or spray), and you can choose your level of gloss. Though personally I'd want to be absolutely sure it the pyrite was super-dry first!

[Don Lum]

[robhanson]

Thanks again for the answers. My wife and I were talking about them today and had thought of the silica as well, we've just gone ahead and bought some online. I'll then take them to work (a chemical site) and put them in a lab oven/incubator for a while. Once they're dried out I'll put them in individual ziploc bags with a silica sachet until we decide what to do with them. I think eventually we'll put them in a box frame, but if we do that I'll make sure to make it airtight and add silica into it. I just took another frame with some in over the weekend and found that the one small pyrite ammonite in it was falling apart, very glad I found this now before it happened to the big ones I recently found!