Caring For Mineral Specimens
Posted by: Raymond McDougall on 12.06.2013 | Filed under: Collectors

RealgarI thought of various titles for this post. “How to Not Kill Your Minerals” sounded a bit harsh, even if that is what this is about and people do it every day. “How Looking After Your Minerals is Like Looking After Your Dog” came close, but seemed a bit long and I really wanted to make sure it was obvious what this post was about. It’s important stuff.
When you have a mineral specimen in your collection, you have something beautiful, valuable, and of significance in natural history (and maybe human history too, depending on its story).
You are a custodian. We all are. Our role is to preserve and protect them, and pass them on some day. If you take this to heart, you are a curator.
Even if you have only a single specimen, or a select few, it’s a nice role to have. But it’s also a responsibility.
Maybe you’re wondering if I am perhaps taking this a little too seriously, and whether I’ve hit myself with a hammer too many times (Well, answer to that: Yes. Ouch, ouch, ouch.) After all, mineral specimens aren’t beloved pets. They don’t need feeding and they won’t run out and get into mischief if the gate is left open. (True, but Fido isn’t going to tarnish from his beautiful original colour if he sits out in the sun, he won’t fall apart in water, and he won’t disintegrate if it’s a bit humid in the house…)
Minerals are not alive, and it’s fair to point out that they have survived for up to millions of years before we have the privilege of looking after them. However, minerals have grown in a very specific environment, and have been preserved in a specific environment ever since, and as soon as they are out of that environment, things can be very different. Care is needed, at each step along the way, once a specimen has been extracted from the ground and prepped for a collection.
Many of your favourite minerals will not survive as they are, unless you look after them. Examples: fluorite, barite, pyrite, quartz (amethyst), gypsum (selenite), topaz, fluorapatite, celestine… the list goes on.
The example photographed above is a specimen of realgar crystals on orpiment from Quiruvilca, La Libertad Dept., Peru – both minerals  are incredibly soft and can be scratched by a anything harder than a feather (almost, anyway), and both are unstable and disintegrate over a period of time, with particular sensitivity to light, long exposure to which accelerates the process. These minerals should be handled/moved as minimally as possible, and stored in the dark – they will otherwise turn to powder before long. Even so, exposure to air plays a role in the process, but looking after them the best we can will at least prolong their existence as stable mineral specimens. It is not always easy to find information on every mineral, but when in doubt, I err on the side of caution and keep specimens protected, out of strong light (or any light until I know more), in a relatively dry climate-controlled space.
The best advice I have is: read and learn all you can. I am always learning more about this.
1. Physical Transportation
Sounds so basic, I know. But do you know how many people mess this one up? It’s enough to make you cry. I think it’s safe to say that somewhere in the world a mineral specimen gets damaged in transportation every single day. Crunch. It sure contributes to the difficulty of finding damage-free specimens for collections. Really, every time a mineral specimen is moved at all is a chance for damage. But whenever you are transporting a mineral specimen, whether it is from the field back home, or from a mineral show or a trip, mineral specimens need to be wrapped very carefully, each specimen individually. (Never let a specimen rub against another one unless you don’t care if they come out at the other end looking like specimens that just spend time in a box rolling around on each other!) If a specimen is particularly fragile, individual steps must be taken to transport it, and all sorts of techniques may be used. For typical specimens, paper towel and then newspaper will often suffice, but err on the side of caution.
2. Handling
Although we think of “rocks” as durable things, many minerals are incredibly fragile and many are also very soft or otherwise surprisingly vulnerable. Crystals of some minerals, for example gypsum (often referred to as selenite) are so soft that a fingernail will easily scratch them.
Another example, some specimens of orpiment will be damaged by the pad of your finger. Some minerals are very sensitive to heat, including the heat of display lighting or even just the heat of holding them in your hand – cerussite and sulfur can be common examples of this. Some minerals are very sensitive to oils we have on our hands, so one fingerprint that is not immediately cleaned off can leave a permanent record, for example on a nice pyrite crystal. In general, it is good specimen-preservation practice to handle specimens minimally until you’ve read about them. Many minerals are durable enough that no amount of handling will affect them -until you drop them on a hard surface, anyway. But all minerals are different.
3. Housing/Storage/Display with Adequate Space
Mineral specimens should be housed in enough space that they are separated from one another. They should never be so close as to be touching each other – that’s a sure way to damage them. If they are in drawers, each specimen should be well separated from the next, ideally in a separate specimen box.
4. Light
I love sunlight. But many minerals hate it – probably more than you have in mind. And these are common minerals you will absolutely have in your collection already or some day.
Sunlight is destructive to many mineral specimens. Some specimens will irreversibly turn dark, such as proustite or pyrargyrite, which will become nearly black (on very little exposure – keep these out of sunlight at all times and store them protected!). Vivianite will darken and deteriorate. Realgar too. Many specimens will fade from their vibrant colours to pale ones, or even lose all colour – examples include amethyst, fluorite, barite, celestine, some fluorapatites, topaz… and there are many others. Sulfur, cerussite and other heat-sensitive minerals won’t thank you for sunlight either! Do your best to learn about light sensitivity, but in general, many minerals should not be exposed to direct sunlight for any length of time, and should certainly not be in a display case in direct sunlight.
5. Water
Many minerals are water soluble! Cleaning them in water will spell certain doom.
Years ago, a woman bought a very nice specimen of  Saskatchewan blue and purple halite (rock salt) from me at a show, and I always told everyone to be careful with them – absolutely no water. She came back the next year, apparently having forgotten, angry and wanting a refund since she dissolved her halite in the kitchen sink. I just felt badly for the halite.
A surprising number of mineral specimens should NOT be cleaned in water. One common example is gypsum (also referred to as selenite) – it won’t dissolve, but the lustre will dull over time.
Another example is pyrite in matrxi from Navajun, Spain – the pyrites don’t mind water but the matrix will fall apart, dropping the crystals out.
Be very careful with water and mineral specimens – always read mineral literature and online before you subject your minerals to anything – because you may inadvertently be torturing them!
6. Moisture/Humidity
This really goes with many of the same minerals susceptible to the water issue, but this one is a lot more subtle. In general, many minerals that have formed in arid conditions – salt lakes, with the borate minerals, for example – will not do well in even a decently conditioned mineral room if you are located in a more humid climate. Unfortunately, this often means that those of us who live in humid or semi-humid places in the world just can’t collect all minerals – some just can’t survive it. There are other minerals that tend not to do well in humid conditions, even if that might not be evident from the chemical composition of the mineral itself – some sulfide minerals, notably marcasite, pyrite and pyrrhotite, can decompose in humid conditions – always store them in a dry place.
7. Bacteria
Believe it or not, there are certain bacteria called acidithiobacillus ferrooxidans that are known to love pyrite – they accelerate its decomposition (and that of marcasite, and pyrrhotite) by metabolizing iron and sulfur to create sulfuric acid. Just what you always wanted! Humidity also plays a key role in this process. Some pyrite, marcasite ad pyrrhotite just seems to decompose no mater what you do to try to protect it (colloquially this is sometimes referred to as “pyrite disease”). Many specimens of these minerals, on the other hand, are fine.
If you have a decomposing pyrite, marcasite or pyrrhotite on your hands, you should isolate it in a dry airtight container or get rid of it altogether. If any acidithiobacillus bacteria are accelerating the deterioration, they could impact other pyrites and other iron sulfide minerals in your collection if not eradicated as soon as possible. Various treatments have been used – if you are interested in what has been attempted, there is a thread on – but these attempts have met with marginal to limited success to date.
8. Other Minerals
Some minerals don’t get along. Just like Fido and the dog down the block. I suspect there may be more examples of this phenomenon, but the one that jumps to mind is sulfur – your native silver specimens should not be together with native sulfur specimens, as the silvers will tarnish black.
9. Older Display Boxes
Some mineral boxes, particularly much older versions of the typical white cotton-lined cardboard boxes, may include acids in the papers comprising the box (same way older papers in books deteriorated). Best to keep an eye on things in your drawers – if a box seems like it might be discolouring, it could be interacting with the specimen it contains (not in a good way) and I’d replace it. I would expect to see such an issue primarily with sulfide minerals – the only time I have ever suspected this issue among minerals I myself was keeping in drawers was a specimen containing sulfide minerals.
10. Cataloguing and Display Techniques
Be careful as to what you attach to your mineral specimens! Many glues and other substances (such as might be used for affixing or painting on a catalogue number) do not come off specimens without difficulty, or at all!
In general, never use any silicone or any epoxy. If you are using glues, use ones that can be removed – hot glues and white glues.
11. Display
To me, the subject of caring for your minerals does also encompass the way in which you share them with others, and even appreciate them yourself. I would give this some thought as soon as you can in your collecting career – whether this is one shelf, or a display case or two, or drawers, or a room or larger space with many of these things (it will be the latter, one day, believe me), show them well. Good lighting is paramount, and make sure you aren’t overheating your specimens. 50W low voltage halogen are one fairly good way to go (as long as you have some ventilation for the lights and the case), and LED lighting systems are improving all the time, as are other systems, so keep your eyes on different developments.
And finally, if your specimens are displayed on open shelves or in cabinets that are not relatively sealed, dust will be a consideration too – some level of enclosure is really helpful.
Unless you are totally successful with enclosure (careful of the heat), some amount of periodic dusting and cleaning may also be required, and when you go to do that, don’t forget to be careful about what each mineral does and doesn’t like! No hot water for the heat-sensitive, and no water at all for others, no sulfur with your silver, no sunlight… Maybe it really is a bit like looking after Fido.