FMF - Friends of Minerals Forum, discussion and message board

[John S. White]

Jordi

A friend of mine wants to know how to clean up and make shine the wonderful pyrite cubes from Navajun, Spain. I assume that you are an expert on this subject, so please share this information with your faithful audience, if you will.

[Jordi Fabre]

John,

Is not an easy answer to this question. Pyrites are brilliant or not brilliant according the conditions of formation as well as the oxidation process suffered by them in the mine.

If they are naturally brilliant you don't need to do nothing and it is still better don't do nothing. If they are dull or oxidized then all process have some risk, because the Pyrites could have natural microcracks where the chemical substances used could remain after the process and then do some slow internal damage that will appear after a while in form of "explosion" of the Pyrite.
I'm sure that you are familiar with these Pyrites on old collections totally destroyed and converted in iron dust (and leaving free sulfur during the process that unfortunately tends to collect the atmospherisc H20 being transformed in Sulfuric acid vapors).

To simplify the answer, the less risky if you want to clean Pyrites from Navajún could be to use Oxalic acid. You can find out all details about the Oxalic's procedure using this excellent page, partially wrote by Pete Modreski!:

https://www.agmc.info/cleaning_tips.htm

If the final result is not satisfactory I suggest to you don't do much more, as any other process could generate a worst result than the actual state of your friend's Pyrites.

Maybe some other member of this Forum could suggest other tips but honestly and by mi experience, to clean satisfactory Navajún Pyirite is not so easy and it could give a lot of unsatisfactory surprises.

Hopefully it helps.

Jordi

[yowanni]

I remember that some years ago, the owner of Ambasaguas recommended me to break and grind a piece of matrix.
After it's necessary mix with a little water to make a paste.
Finaly you must rub the pirite with the paste.
It's going to make the pirite very shining.

(Sorry, I don't speak english fluently.)

[Jordi Fabre]

Good suggestion. Unfortunately, by my own experience, the Pyrites cleaned on that way don't stay briliant for long time, and also I'm afraid that on some cases this process makes them decay a little bit faster than if you don't use it (but pretty slowly, not panic)

Jordi
PS: please note that I live in Barcelona where the humidity is really high. On dry places, Pyrites have not problems.

[yowanni]

I recommend this procedure if the pirite is naturaly oxidated.

I live in cantabria, in the north of Spain and the humidity is near 90% all the year, and the pirites from Navajun are realy well.
And by the time i did not need to clean the pirites.

[Pierre Joubert]

I have a few flats of pyrite from Navajun. In one of the flats some pyrites developed a thin white coating that can I can remove with my nails. What is the best way to remove this 'chemical'?

[James Catmur]

Pierre

I just use my finger nails. I have never tried another approach

James

[Peter Megaw]

You might try softscrub on a soft toothbrush. It uses gypsum as its cleaning abrasive so it should polish without surface damage. Once the piece dries thoroughly you can soak it in high strength isopropyl alcohol to kill any bacteria...then let that dry thoroughly.

Once there is significant surface damage from acid the luster cannot be restored.

[Pierre Joubert]

[Pierre Joubert]

[Philippe Durand]

I use a product designed to clean kitchen cooking platina, copper pans, and silver knives. Its a solid mixture of soap, vegetable oil and mainly clay, with a small amount of water. It makes a paste and the result is perfect.

After removing the paste, you can dry with alcohol or with a hair dryer.

Ask to your wife, she may know

[alfredo]

My recently departed friend Rock Currier imported many tens of tons of shiny pyrite crystals from the Huanzala mine in Peru. According to Rock, considering tonnage of one mineral species from one locality distributed in collections worldwide, Huanzala pyrite holds the world record for most abundant mineral specimen and, according to Rock, all of it is cleaned with hydrochloric acid (HCl) by the Peruvian dealers. So apparently, at least for that locality, HCl leaves them nice and shiny and undamaged.

[James Catmur]

Pierre

I have always assumed that it is just a very thin layer of the chalk marl that the cubes are found in. But I could be wrong.

James

[Pierre Joubert]

Hi Phillip, your advice is very much the same as Peter's. Thank you.

Thank you Alfredo. Very interesting. I will remember that.

Thank you James.

[Ivan Blanco (PDM)]

Sorry Pierre, I just have seen your message. The coating around the pyrite cubes of Navajún (and some others from La Rioja) is cookeite. They have been studied and the results published.

Most of these coatings can be removed with your finger nail or a brush. The use of a water jet gun make the work very easy. If the cubes are on matrix, do not use water, just a soft brush.