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Techniques for CollectorsRemoving shale matrix from pyrite?

23rd Jul 2006 19:42 UTCThomas Morrow

Hello Everyone,

I have some pyrite specimens from SE Missouri, USA. They were found in a road cut through a shale layer. The shale seems to be an oil shale (it smells like oil when struck with a hammer). Some of the specimens still have the shale embedded among the crystal terminations. I have been able to flake off most of it with a dental pick but I cannot get it out of the smaller crevices. Does anyone have any tips or tricks to remove the shale and expose the smaller crystals?

Thanks & Regards,

Thomas Morrow

Bentonville, Arkansas

4th Aug 2006 22:01 UTCThomas Morrow

Hello,

Thought I would post an update. I am making slow but good progress with a heavy duty ultra-sonic cleaner.

Regards.

8th Aug 2006 20:29 UTCWilliam G. Lyon

One possible addition to consider: use salt solution (NaCl) to assist in the ultrasonic dispersal of the clay. Changing any swelling clay layers to the sodium form should allow them to expand and soften. This won't work with illite, but may help if some of the layers are still smectite (esp. montmorillonite or beidellite).

8th Aug 2006 22:53 UTCThomas Morrow

Thanks, I will give that a try.

Regards.

10th Aug 2006 22:43 UTCJohn Makohon

hydrating and allowing the specimens to dry several times should aid in the removal of the shale encountered on you pyrite specimens. Have you tried soaking the specimens in HCL? Often pyrite is found in carbonate rich shales and the acid can degrade if not totally dissolve the shale.

11th Aug 2006 19:45 UTCThomas Morrow

Update:

1. The salt solution doesn't seem to affect this particular shale. :(

2. I have tried soaking for up to 2 hours in HCL. This doesn't affect

the shale either. It does remove the tarnish from the pyrite.

3. As part of initial cleaning I have been soaking the specimens in

a solution of dish soap and water and then drying. This seems to help

loosen the shale. I have been repeating this several times.

4. Here is the cleaning regimen I am currently using:

a. Soak specimens in solution of dish soap and water.

b. Dry specimens.

c. Flake off shale with dental pick.

d. Rinse and brush with nylon brush.

e. Repeat steps a-d several times.

f. Ultra sonic cleaner using solution of laundry detergent and water.

I run the cleaner continuously on a timer 30 min. on, 45 min. off to give the transducer a break.

g. When solution gets dirty. Change solution.

h. Dry specimens.

i. Flake off shale with dental pick.

j. Repeat steps f-i until specimen is cleaned.

h. Soak specimens in oxalic acid solution for 30 min. to 1 hour to

remove tarnish.

i. Rinse with water.

j. Nylon brush and clean with soap and water.

k. Brush wet specimen with old toothbrush and whitening toothpaste to

help shine it up.

l. Dry specimen. I now have a sparkly clean piece of pyrite.

This procedure is averaging about 2-3 days. A stronger ultra sonic unit might speed up the process but I am using a fairly heavy duty unit (the 1.5 quart heavy duty model from Harbor Freight). Any additional suggestions,

especially about ultra sonic cleaning solutions would be most welcome.

Thanks and Regards,

Tom

12th Aug 2006 06:02 UTCDon Saathoff Expert

Tom, I call it "pickin' and grinnin'"....with some matrix, thats all you can do....there ain't no panacea!!!

14th Jan 2007 15:21 UTCCharles Brisco

A Low Tech Method

1) Place the pyrite in a small amount of water

2) Freeze

3) Thaw and lightly pick loose shale off.

4) Repeat freeze process as many times as necessary

24th Jan 2007 23:54 UTCAnonymous User

Hi there!

Pyrite is dissolved(as far as I know...)only using Nitric (Azotic) Acid- HNO3.Feel free to use HCL (I think it only cleans the specimen). and try H2SO4-Sulfuric Acid.This awful "monster" solution is very dangerous,so be carefull!I have cleaned Quartz with Pyrite and no (visible) damage done to the Pyrite,and according to my knowledge the Pyrite is not affected Chemically by the Acid.

You'll need a specialist's opinion on what I'm gonna say now,but,probably,the tarnish effect by the HCL is because your speciments have a light film of rust upon them(if so,they should look more golden-red than golden-silver like Pyrite is).If you leave the acid act one day or so 4 water to 1 acid for one day or so,it may clean the rust AND the matrix.Two hours are short tim!

If you have specimens to sacrifce,try Aceton,tooth paste or even Nitro-Cellular Dissolver(you can find these in a wall-paint store).

To be more effective mechanically,use a tooth brush.Use scissors to cut the brush hair and shorten them to half their normal lenth.This will make them less elastic and harder.Fell also free to use a needle,Pyrite Hardness is 6,kitchen knive hardness is 5.5,a needle has to be less,so you don't damage the specimen.

Be careful with these nasty acid and use masks!

-Kostas.

25th Jan 2007 01:37 UTCAlbert Mura

Tom, I know you don't want to hear this but any contact with pyrite and acid (any type) is not good. It may look great when you are done but wait it will decompose. I have had the same problem with pyrite nodules fron New York. Sonication is the only thing that works. I use Alconox in the water instead of your dish soap, it is on the basic side. In any case I can not stress enough the use of acetone to dry the pyrite when you are done. Certain pyrites like those fron Spain or Peru are stable but most others will break down with time in a moist atmosphere. Since we are on the subject of pyrites, do you have any from your location you would like to trade? Al

25th Jan 2007 18:02 UTCAnonymous User

Hi all!

Al,are you sure any acid will harm the Pyrite?I've used even HNO3(that is supposed to dissolve the Pyrite)and no damage done(ok,with the Nitric HNO3 I saw some troubles like change in color after a day in the acid,but nothing more.)HCL and H2So4 caused no (visible) damage to my Pyrites.If there is any sign that I could find as a clue my Pyrites are damaged,please let me know(an examination under a loope for example!)

By the ways,yes,I have some Pyrites for trade from Madan,Bulgaria.I will trade for intersting specimens of Quartz(since I'm building this kind of collection right now),but after 2 weeks or so,since now I'm very busy with my exams.Al,please contact me at daus_fr@hotmail.com,if you are interested :)

Cheers!

-Kostas.

25th Jan 2007 20:40 UTCJoseph Freilich

hi,

just be careful of what lies underneath the shale...sometimes you dont want exposed what the shale is hiding...

cheers, joe

25th Jan 2007 21:01 UTCAlbert Mura

The main decomposion pathway for pyrite is via acid (acid run off from mines is caused by pyrite). Some pyrite doesn't even need the acid it will generate it itself (H2SO4) on contact with moisture. Any acid will cause the pyrite to break down from a thermodynamic point of view but kineticly this may be slow (years depending on the pyrite and its structure). You may not see any damage now but time is not on your side. If you use it let the specimen sit in bicarbonate solution to neutralize the acid then pure water. But again use acetone to dry it as good as possible. Al

25th Jan 2007 22:18 UTCAlfredo Petrov Manager

It is a common misconception that neutralizing the acid emanations from pyrite will prevent or impede further decomposition. This is mistaken; neutralizing the acid will speed up the decomposition! If this sounds counterintuitive, consider the following: The sulfuric acid oozing out of the cracks in your pyrite is a byproduct of bacterial metabolism; neutralizing it does not kill the bacteria, it merely removes their waste products so that they can then flourish and generate more acid. A nice soak in HCl, on the other hand, is quite uncomfortable for the Thiobacillus critters in your pyrite. I soak my pyrites and marcasites in strong HCl and then give them only a brief rinse before mounting the newly shiny sulphides in a plastic box. Not a permanent solution, but they stay brighter a lot longer than the ones I tried to neutralize.

25th Jan 2007 22:31 UTCAlbert Mura

Alfredo, what you are saying is true, however, the bacteria is not always present. Thermodynamicly pyrite is not stable to acid. The bottom line is many pyrites in collection have decomposed because of moisture that generates acid even if the bacteria is not present. The key to this is moisture.

26th Jan 2007 03:18 UTCAnonymous User

Hi all!

May I suppose a solution?First kill any (probably existing)bacteria using Antibiotics,then use a concetrated solution of Sodium Bicarbonate to neutralize any Acid.

Is that right?Could this be done?

Cheers!

-Kostas.

26th Jan 2007 16:51 UTCAlbert Mura

I believe the use of antibacterials have been tried. The sad thing is once decomposion starts on pyrite there is little you can do except remove it from the rest of your specimens. This is an age old problem, if you do a search you will find many things have been tried. This is a real problem for those who collect fossils since many of them have been replaced by pyrite. It is interesting that some pyrite as I have mentioned is very stable (like the spanish cubes). In the case of fossils, some museums use a weak solution of super glue after cleaning not that I am suggesting that for a mineral specimen. You can buy it on the internet its called PaleoBond. I have tried it on a very specimens that have already started to break down just to experiment. I first cleaned the specimens then treated with triethyl amine to remove acid then spoaked in acetone, that way water did not come in contact with the specimen. Then soaked it in PaleoBond. Now I have to wait to see if this stops the decomp.

17th Jun 2007 17:08 UTCRock Currier Expert

Thomas,

The solution to your pyrite cleaning problem is not a chemical one. You need to get a sand blaster that is using glass beads and not quartz sand. You will be able to clean your specimens much faster with this technique. I have cleaned thousands of pyrite specimens with air abrasive techniques and it works quickly and well. The pyrites you are cleaning are not very valuable, so you don't even have to exercise much care in their cleaning. Find a metal finishing shop or a shop that has a sand blaster for cleaning sparkplugs and see if you can use one of their sand blasters. You might have to buy some glass beads though and change out their garnet or sand abrasive media for your work, but it will save you many many hours of work.

Rock

20th Nov 2007 21:36 UTCMike Palescuk

Is acetone completely safe to use on Silurian era (New York) Rochester Shale fossil fauna without harm? I am concerned that acetone submersion may dissolve the shale or damage the very thin calcitic outer shell material of a fossil.

24th Jul 2012 18:39 UTCAndrew Zioto

As you can see from the attached image I have figured out how to clean pyritized fossils in shale.

I find these in western new york. Using the method below i have cleaned hundreds of them, and they still look nice and shiny.

What you need:

- 5 gallon bucket

- strainer

- rubber gloves

- face mask

- well ventilated space

- towel you can ruin

- nail brush

- throw away electric toothbrush $5

- Iron out ($14/bottle (dry powder)

- CLR $10-$20/bottle depending on size.

Cleaning method for round nodules of different sizes when you don't want to preserve the matrix:

1) Soak them for a day in water (soften up the shale)

2) Emerge them in a extremely concentrated solution of Iron out. fill a 5 gallon bucket with 3 inches of water and pour in at least 2 cups worth. once you stir it in, the water needs to become clear, or you need more water. soak the nodules in the Iron out for a few hours. Pour them into a strainer. Wearing gloves, cover them in dish soap and massage them together under running warm water. your want them to lightly grind against each other, this will cause most of the shale to fall off and not damage the pyrite. once the soap is all gone, dry them off, and rub each one with a towel (takes time but makes a big difference)

3) Repeat step 2 once more.

4) Soak them in CLR for a few hours. Wash them off good, and than buff with a towel. Shale might still be present in the cracks, if so use the pointy end of a tack to remove it, then soak in CLR again.

Method for cleaning odd shaped nodules when you don't want to preserve the matrix:

1) Soak them for a day in water (soften up the shale)

2) Emerge them in a extremely concentrated solution of Iron out. fill a 5 gallon bucket with 3 inches of water and pour in at least 2 cups worth. once you stir it in, the water needs to become clear, or you need more water. soak the nodules in the Iron out for a few hours.

3) using a nail brush or a electric toothbrush scrub the bejesus out of them to remove the shale, rinse constantly under water to see progress. use the end of a tack to remove shale from cracks/ around the edge of exposed fossils. You will need to repeat step 2 many many times until you have removed the shale.

4) Soak them in CLR for a few hours. Wash them off good, and than buff with a towel.

Method for cleaning pyritized fossils you WANT to leave in the matrix.

1) dip toothbrush in iron out and scrub. rinse briefly under water, dry and repeat, over and over and over. if possible set up your piece in a dish so that only the exposed pyrite is exposed to the iron-out solution, then scrub it every hour or so. change out the iron-out solution ever few hours. Once you have most of the tarnish removed, use CLR on it instead of iron-out.

24th Jul 2012 21:27 UTCRock Currier Expert

I would think that acetone would effect only perhaps some of the organic things in the shale and would not likely hurt the shale or the fossil. But, what ever you do, try it our on a piece of rubbish before using it on good specimens.

24th Jul 2012 21:39 UTCKelly Nash 🌟 Expert

Andrew, have you tried using a high-pressure water spray gun? I've had pretty good luck with some dense black shale imbedded in pyrite crystals from SE Nebraska. It's slow going, but quite a bit faster than brushing.

25th Jul 2012 12:59 UTCRock Currier Expert

Probably the easiest first line of cleaning of pyrite concretions in shale these days is to hit them with high pressure water from one of the new little fabric guns. Often soaking them in water to "loosen up the shale" would be worth trying. If that does not work, then chemical or air abrasive units with glass beads can be brought into play. The cleaning of pyrite dollars from Illinois used to be a very tedious process before the general use of air abrasive units.

25th Jul 2012 13:51 UTCRobert Farrar

The paleontology world uses heavy wetting agents (detergents) to disaggregate shales and free fossils from argillaceous matrix. I don't know specifics regarding availabilities, but look for Quaternary-O or Rock Quat names. There are some technical articles about their applications. Both are ammonium based, so I don't think they should harm pyrite. Their normal use in a paleo lab, would be to free carbonate fossils from gray/black shales.

Bob

25th Jul 2012 14:17 UTCBob Harman

I have used a hi pressure dry cleaning gun on my pyrite nodules from the Harding St. Indianapolis quarry with great success. Soak in water overnight and then blast away. Only exception might be those specimens on an esthetically nice piece of shale matrix as I have included here. Pyrite nodules on matrix are unusual as the shale largely flakes off. Thus, good matrix specimens command a premium. CHEERS............BOB

7th Aug 2012 14:00 UTCAndrew Zioto

I am having trouble cleaning some recent finds recovered from extremely dense shale.

Andrew, have you tried using a high-pressure water spray gun?

i used my friends and honestly it didn't do much to remove the shale.

i tried acetone... nothing (made it feel cold).

iron-out ..... nothing (except the pyrite that i thought was chalcopyrite now looks like regular pyrite)

CLR ..... nothing

The shale containing the 0-1inch nodules is very fractured and splits nice and easily. these nodules clean up nicely with iron-out and CLR.

However, if you go down a few inches, it doesn't have any defining "split" lines. It resembles more of a metaphoric texture and is as dense as Dolostone. I have to use a 12 lb sledge hammer and a pile of wedges to make a dent in it. 1-3 inch nodules and complete fossils in perfect condition make up for the back breaking work required to get them out.

Basically the shale is soooo dense that high pressure sprayers don't do much. Even chemicals like Iron-out are not able to penetrate the shale to much success. I bought some dental picks from a dental supply company in town that really helped ... until i broke them (its that tough).

I'm determined to get these looking awesome. but i feel like i need some restricted-chemical or something that's going to cost a small fortune. Any ideas?

8th Aug 2012 10:09 UTCRock Currier Expert

I don't think chemical reagents will solve your cleaning problem. You have lots of hard shale to remove and mechanical means are going to be your main method of making nice specimens. Since you can clean them, sort of, with dental tools you just need to get more aggressive. Get some of the little hand held pneumatic hammer drills, preferably with tungsten carbide chisels or points of different sizes to hog off most of the matrix. Switch to smaller ones when you need to do fine work near the pyrite. Probably the last bit of clean up you will need to do will need to be done with a micro abrasive tool using glass beads of high pressure water will not remove the shale.

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