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Cleaning Fluorite

Posted by MG  
MG
Cleaning Fluorite
September 11, 2004 09:50PM
I have a nice specimen of fluorite that has a layer of calcium carbonate, or hardened mud on it and I'd like to get it cleaned without damaging the specimen. Any help? I was told a high powered water blaster might work.
Lloyd L
Re: Cleaning Fluorite
September 11, 2004 10:47PM
If it's mud, a high pressure water gun (sprayer or washer) should work.
If it's calcite, you'll need some sort of acid. Any acid will work, but you have to consider what it might do to the rest of the specimen and the risks involved to your well-being. Although organic acids such as acetic (vinegar) or citric should work eventually, inorganic acids are faster but present a greater health hazard. Commonest seems to be hydrochloric but many people favour phosphoric as this also has the beneficial side-effect of working on iron-stains too. Phosphoric acid is available in domestic rust-removers such as 'Jenolite'.
If too strong an acid is used, it can etch the fluorite.
Whatever method you use, please, please be very careful and if you are not used to, and have no proper facilities for, handling acids, get some expert assistance. You should also wear eye-protection if you go down the high-pressure gun route.
Hope this helps and you end up with a worthwhile, gemmy fluorite.
Lloyd
Peter Haas
Re: Cleaning Fluorite
September 15, 2004 01:56AM
Be careful with mineral acids. They will convert fluorite to hydrofluoric acid to some extent, especially when used at higher concentrations. The fastest way is not the best way here. Phosphoric acid and sulfuric acid form calcium salts that are less soluble (more stable) than fluorite, so they will attack the fluorite to some extent even when they are dilute. This doesn't men that your fluorite will dissolve to any visible extent, but the brilliance of the surfaces might be gone after the treatment. Acetic acid is the best choice. Citric acid is a good complexant for calcium and, therefore, will attack the fluorite as well.

A water gun is also not a good advice: fluorite is sensible to temperature and mechanical shocks, so the crystals may crack. Mud is more efficiently removed by soaking in water for a couple of days. It often consists of clay minerals or of ill-defined metal oxides/hydroxides. They can adsorb considerable amounts of water, which makes them swell. However, adsorption is a physical process and hence, rather slow, so it will take some time.
Lloyd L
Re: Cleaning Fluorite
September 15, 2004 06:26PM
Thanks, Peter, I stand corrected.
More science and less brute-force is always a good policy!
Lloyd
Gunnar Färber
Re: Cleaning Fluorite
September 24, 2004 07:26AM
Hello,

if you have only Flourite there, you can clean it very well in HF. But please HF works good but is also very dangerous.

Best Regards

Gunnar
PeterA
Re: Cleaning Fluorite
September 24, 2004 12:00PM
Hi Gunnar,

HF is not only dangerous, it's lethal in quite small amounts - even as a spill on bare skin (clothes soked in acid might even be worse). If skin are exposed and not washed/threated with special lotion (I think it's some kind of Ca-ionic lotion that neutralize the HF) after a short time after the exposure, the damages might cause a painful and slowly death!

I was presented an article when I started work in the laboratory at university about a tragical death caused by HF (I think it was about 1dl, on less than 150 square-centimeters of skin!). I never worked alone on the lab with HF after that! So nobody should even consider using HF outside a well secured labb with easy way to get treatment and help if the accident should happen!!! Even very smal exposures on skin should be treated by doctor.

Regards
PeterA
Danny
Re: Cleaning Fluorite
September 24, 2004 12:24PM
The solution comes in a gel form and is calcium glauconate. It costs about £25 for a small 25g tube. But even this isn't really an "antidote". I'd advise against against using HF unless in quite controlled surroundings.. ie. a fume cupboard, full safety gear, a nearby shower for irrigation in case of a spill and obviously some calcium glauconate gel. In fact for the sake of a clean specimen id probably advise against using it fullstop. Nasty stuff!

Danny.
Danny
Re: Cleaning Fluorite
September 24, 2004 01:24PM
Sorry... Calcium Gluconate.. available from IPS healthcare as well i others i expect.
Alfredo
Re: Cleaning Fluorite
September 24, 2004 01:42PM
Available in the USA from www.attminerals.com
Chris van Laer
Re: Cleaning Fluorite
September 30, 2004 03:00PM
Fluorite is soluble in sulfuric acid (concentrated) and releases hydrofluoric acid in the process, so it's best to avoid this altogether. Fluorite is NOT soluble in hydrochloric (muriatic acid), especially in a dilute solution. Use only cold, do not heat, and allow to soak until all bubbling ceases. It is very important to properly neutralize all traces of any acid after even a short bath; this is easily (* and cheaply) accomplished by soaking for an extended period in a solution of common baking soda and water. This may liberate some carbon dioxide gas, so do not seal container, but allow gases to escape. Also, the dissolution of any iron compounds present will color the HCl yellow, which can soak in cracks and crevices or porous minerals and discolor the specimen yellow. This can be reversed if not allowed to completley dry out; if yellowing persists, allow longer neutralization in baking soda or soak in a solution of sudsy ammonia for as much as a week or two. If still yellow, soak in a bath of warm or hot oxalic acid; this will dissolve traces of iron chlorides, the follow with a soak in baking soda solution.
Peter Haas
Re: Cleaning Fluorite
September 30, 2004 03:22PM
Two comments:

Fluorite and HCl: Concentrated hydrochloric acid DOES attack fluorite to some extent (which is easily confirmed by the SiF4 test). The reaction is very slow and it is certainly not dissolved to any visible extent. Its brilliance may be lost, however, when it is exposed to the acid over a longer period of time.

Calcium gluconate and HF: An effective neutralization requires that the gluconate is applied immediately after the contact. This is a big problem, though, because HF is a rather weak acid. It does not etch the skin, it simply penetrates through it. There is big risk, that you don't notice anything, when you spill a small volume over your it. There are well documented examples of people who died within a few days after their hands or forearms had been contacted with a few milliliters of hydrofluoric acid for a short period of time.

Peter
Alfredo
Re: Cleaning Fluorite
October 01, 2004 12:16PM
Re Fluorite and HCl: Peter says "Concentrated hydrochloric acid DOES attack fluorite to some extent..."
This is true, but irrelevant to mineral cleaning, which is normally done with less than concentrated HCl. In fact, for many cleaning purposes, somewhat diluted HCl works better than conc. HCl.
Peter Haas
Re: Cleaning Fluorite
October 01, 2004 03:34PM
Alfredo,

That's right. But - do we know whether people who are posting here, have ever handled chemicals before ? Could we preclude that they simply don't know that there are less and more appropriate concntrations ? They'll likely play around with the chemicals they use: for instance, they will find out that increasing the concentration will speed up the process. People tend to become impatient when they have to wait every time for something to happen, so this apparent advantage will overweigh any precaution - especially, if you don't know much about chemistry: you'll never be going to think about side effects - unwanted competing processes that become dominant at higher concentrations, or a complete change of the chemical and toxicological properties, for instance - and even less about the hazards. I still remember a cleaning advice proclaiming the use hot concentrated sulphuric acid, given by someone in this forum a couple of months ago ... and that's another important point: heating speeds up some chemical reactions, while others are almost not affected. When minerals are cleaned, desorption and displacement processes at phase boundarys do often play an important role. These are physical processes and they respond to different parameters than chemical reactions do. The speed of action of an oxalic acid solution on iron stains, for instance, is higher when the solution is permanently stirred (of course, this is a bit problematical, when the specimens are in it) than when it is heated.

Actually, I have to be aware of all that when I recommend a particular chemical. I also have to be aware that there is always the risk of a hazard, when people are not used to handle chemicals. Therefore, I have to recommend working conditions that are safe enough for not seriously hurting a person and not imparting any permanent damage in case of an accident. I certainly can't guarantee for that when the chemicals are used at different concentrations or in different conditions and, therefore, I have to tell people what may go wrong if they don't exactly follow the advice. I will be fully responsible if something happens what I didn't point out. The most common reason for misuse of chemicals is ignorance. Of course, It's their own decision to use chemicals, but I can't expect them to act responsible, when they have not been informed about any imagineable risk.

Many people think of chemists as eiher acting irresponsible, or grossly exaggerating. The latter might be the reason why many collectors are more easy to convince, when they're told that there is a risk of a permanent damage to their specimens ... There is, honestly, rarely any exaggeration, though.

Peter
Bob Reed
Re: Cleaning Fluorite
October 01, 2004 06:29PM
Hi all,
45 years ago i worked in a steel works for a short time. My first job was to get a bucket of water and a carboy of Hydrofluoric Acid. I was then told to wash some skylight windows!! How times change. Needless to say the job was short lived.
Regards Bob
lynna
Re: Cleaning Fluorite
January 17, 2005 02:11PM
Hi all,
I have mixture of 1g of fluorite+calcite with me.

Anyone here could recommend me any reliable test so that I would be able to know how much of fluorite presence in my 1g of mixture of fluorite and calcite?

One of the possible solution is to clean the mixture with hydrocloric acid but anyone here could give me a clue about the recommended concentration of hydrocloric acid that I should use for this?

Thanks in advane

lynna
David Von Bargen
Re: Cleaning Fluorite
January 17, 2005 04:35PM
A 10% solution is used in testing for calcite and creates a rather vigorous evolution of carbon dioxide. I would suggest that you use a more dilute solution or you could "boil" the fluorite out of the test tube.

If you have an X-ray diffraction machine, you could also do a powder diffraction (with appropriate standards for peak height of pure materials) pattern to determine percentages.
Sergej Martynov
Re: Cleaning Fluorite CaF2
May 19, 2006 12:45PM
Hello, I would like to exchange experiences because of machine cleaning of CaF2 glass
the material does not stand which chemicals, which chemicals doesn't the material bear?
If somebody could help me, that would be super
Re: Cleaning Fluorite
July 29, 2006 07:38AM
lynna: Just weight your specimen, then dissolve calcite in 5-10% HCl and then weight the fluorite. And here we go!
Re: Cleaning Fluorite
August 18, 2006 06:17PM
Everyone has some great ideas and they are helpful, but I do not have the means to use the more "powerful cleaners". Also, I want to ensure my specimen doesn't get harmed. Any ideas of other cleaners to use? My specimens are from the Elmwood Mine (Carthage, Tn USA) and consists of Sphalerite, Calcite, Barite, Quartz and Fluorite and occasional Galena. Its the Fluorite I want to clean up, they have a dust or mud on them. Any help would be great!
Re: Cleaning Fluorite
August 18, 2006 07:20PM
Hi Steven,

One thing you should be aware of is that using liquids with your specimen that vary in temperature from that of the specimen may cause the fluorite crystals to spontaneously cleave off a large piece due to temperature differentials. I used plain old soap and water on a very nice fluorite from Illinois, and because the water was a little different temperature than the fluorite, a corner of the most prominent cube pooped off with a snapping sound.

So use water (or any fluid) that has had the opportunity to reach the temperature of the specimen rather than hot water (or even ice water) on a specimen at room temperature.

I recommend just a simple room-temp soapy water solution and a soft brush - you could let the specimen soak for a while, as someone above recommended - but don't introduce sudden temperature changes or the whole thing could come apart.

JR in WV
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