FMF - Friends of Minerals Forum, discussion and message board

[daviddillman]

I understand Krohnkite is easily dissolved by water. Does this mean it should be stored in an air-tight container? I live in a area (north Texas) where the humidity would be best described as average overall but the summers can be humid. Thanks for your help.

[Michael Shaw]

[Bob Carnein]

I have several pieces of krohnkite from Chuquicamata, some of which go back at least to the 1980s. Until recently, I lived in Pennsylvania, which also has warm, very humid summers. Although I took no precautions, as far as storage goes, that didn't affect the specimens in any obvious way.

[alfredo]

I agree with Bob: it should be stable. Most water-soluble minerals are stable in humid atmospheres; just don't let them get wettened with LIQUID water.

The ones that cause problems in humid atmospheres are the ones that are "hygroscopic" in addition to being water-soluble. Hygroscopic minerals actually pull water out of the air and finally dissolve in their own puddle, destroying themselves and any nearby labels in the process. Luckily there aren't too many hygroscopic species. Krohnkite isn't one of them.

[Pete Richards]

With these potentially challenging minerals, probably the best approach is to minimize their contact with the "real world". Some will dehyrdate and turn to powder, others might absorb water and melt. Pyrite and marcasite will oxidize and turn to iron sulfate dust. One important strategy is to minimize their contact with the outside environment, which brings in (or can bring in) the elements that cause problems, be they excess humidity, lack of humidity, oxygen, or other influences.

Put the specimen in a box that seals tightly and leave it there. I've put some of my pyritized ammonites in slip-top micro boxes and sealed the joint with aluminum duct tape. The exchange with the outside environment must have been decreased by at least 1000 times compared to sitting in an open box. Perhaps this means that the lifespan of these specimens has expanded from 1 year to 1000 years! After that, sorry, but I don't care!

In such a situation chosen for preservation, your specimen will do its best to establish the atmosphere it likes. If it is already very unhappy, it may not survive. But I think this is the best you can do, unless you are a professional geological specimen conservator with very fancy tools that most of us don't even know how to use.

Every time you open the container, of course, the process of creating a "stable" environment starts over. But if the specimen is in an open box, the process goes on day after day, hour after hour. And that's bad!

Alfredo, what do you think?

[alfredo]

I certainly agree, Pete.

About 20 years ago I collected some beautiful gemmy green melanterite crystals underground in Oruro, Bolivia. Melanterite is one of the hardest minerals to keep in a collection - Usually it dehydrates and oxidizes within hours after its removal from a mine. Consequently, despite being a common species, it is present in very few collections; or perhaps is present "only on the label", with the white smelly powder left in its box certainly NOT being melanterite. So I decided to face this challenge and attempt to keep my beautiful melanterite crystals intact. I kept them in a black plastic film container (which used to be ubiquitous, but in this digital age are rapidly vanishing), and kept it in the refrigerator, figuring it was now sealed away from atmospheric exchange, and that the dark, cold environment much resembled its native Oruro adit at 3,800 meters above sea level. Much to the dismay of my wife, there was eventually a whole corner of the fridge dedicated to the collection of unstable minerals.

Results: I only opened the container three times during the last 20 years. The first time, after about 5 years, the gemmy green crystals were still pristine - a major success with this difficult mineral! The next time, after about 10 years, the crystals were duller and had a patchy skin disease. After another 10 years or so, just recently, I opened it for the last time and threw them away - They probably still had some melanterite in their cores, but were too ugly on the surface to be worth keeping. Sniff, sniff (wiping away tears)...

I'm sure most species collectors have made their little check mark in their Fleischers next to "Melanterite", but they don't really have any ;))