Learning Center What is a mineral?The most common minerals on earth Information for Educators Mindat Articles The Elements The Rock H. Currier Digital Library Geologic Time

Minerals by Properties Minerals by Chemistry Advanced Locality Search Random Mineral Random Locality Search by minID Localities Near Me Search Articles Search Glossary More Search Options

The Mindat Manual Add a New Photo Rate Photos Locality Edit Report Coordinate Completion Report Add Glossary Item

Mining Companies Statistics Users Mineral Museums Clubs & Organizations Mineral Shows & Events The Mindat Directory Device Settings The Mineral Quiz

Photo Search Photo Galleries Search by Color New Photos Today New Photos Yesterday Members' Photo Galleries Past Photo of the Day Gallery Photography

Discussions

💬 Home 🔎 Search 📅 Latest

╳Discussions

💬 Home 🔎 Search 📅 Latest

Groups

Recent Images in Discussions

Techniques for CollectorsChalky residue using Oxalic Acid

7th Dec 2016 19:55 UTCNancy Gerlach

HI--

I have to admit I goofed and tried to clean fluorite with Oxalic Acid and now it has a white film on it. Any suggestions on how to remove it? Lesson learned :-S

Thanks in advance-

Nancy

7th Dec 2016 20:19 UTCThomas Lühr Expert

Hi Nancy,

Never ever use oxalic acid on fluorite. Firstly is attacs (dissolves ) the surface of the fluorite and turns it dull. Secondly it produces with the calcium from the fluorite (or from any other source of calcium) a white staining of calcium oxalate, that is very hard to remove, i don't know of any chemical method that does not attac the fluorite. PERHAPS could hydrogen peroxide work. (Anyone other suggestions ?)

Even IF you could remove the staining, nevertheless, the surface is etched and the luster is gone for ever.

Next time please use (depending where you live) Super Iron Out, available in the USA or a mixture of sodium dithionite, sodium hydrogencarbonate and sodium citrate, aka as Waller's solution (google for it).

Thomas

7th Dec 2016 20:52 UTCSteve Hardinger 🌟 Expert

Super Iron out (now called just Iron Out in many places) is quite effective at removing irons stains from fluorite without notable damage. If you try this make sure you use the (Super) Iron Out powder and not the liquid by the same name. The liquid is a completely different formulation.

The Mineral Specimen Cleaning and Preparation forum on Facebook is another excellent place to ask cleaning questions.

7th Dec 2016 21:10 UTCD. Peck

I would hang this one up as a bad experience, and not try to remove the calcium oxalate by any chemical means. The only thing, as far as I know, that will dissolve calcium oxalate is a strong mineral acid and I would not want to possibly produce any hydrofluoric acid in the process. I believe it would take either sulphuric or nitric acid to do that, but I would not want to chance even small quantities of concentrated hydrochloric. (Remember, that oxalic acid produced some hydrofluoric acid with the fluorite.) The quantity would be small, but it isn't worth it.

I have seen several mineral collectors who have claimed that H₂F₂ is Ok to use in dissolving silicates. It is not! It is perhaps the most dangerous acid there is. If you don't believe me, take the time to read this site in its entirety: https://web.utk.edu/~ehss/training/has.pdf Incidently, one of the photos shows a hydrofluoric acid burn from commercial rust remover (brand or type unidentified).

7th Dec 2016 21:23 UTCDana Morong

Donald Peck is quite correct about the hazard of hydrofluoric acid. I did some modest research once and read the small print on the labels of some rust removers at the hardware store. One of them, at the hardware store, was a rust remover meant to clean toilet bowls, and it contained hydrofluoric acid (yes, HF acid, Not HCl). It seems an unnecessary hazard for a household environment (what if the container spilled on the way back from the store?). Anyway, I'd use an outhouse before using HF where I could possibly breathe the fumes. It can have an insidious effect upon humans.

8th Dec 2016 01:28 UTCNancy Gerlach

Thanks so much! Sometimes lessons are more expensive than others times.... but I'm just going to let this one go and next time I'll be a little more proactive about researching before cleaning. One thing for sure is I will never use HF. You guys scared the bejesus out of me about that stuff.

Thanks again--

8th Dec 2016 01:31 UTCNancy Gerlach

I just joined the Facebook group... thanks for the tip!

8th Dec 2016 05:27 UTCJoel Dyer

Nancy, if you are careful, there is - depending on the exact nature of the fluorite sample - a different kind of possibility of saving the sample.

I've used very fine diamond paste to remove various surface blemishes on some samples. Also, I've done this to the scratched plastic headlamps of our Kia car, in *that case* starting from 5 micron paste. Diamond paste can be purchased cheaply via Ebay etc.

You have to use fingers and/or a soft polishing cloth / cotton "ear tips" and try first with *0.25 micron* paste on a small spot somewhere. If this doesn't seem to work, then just forget about it. Don't attempt to use any force or too coarse a paste!

The method has repeatedly worked for myself, who is used to polishing cut sections of minerals for microscope inspection & analysis. Again, I must repeat that a lot of care and patience is needed. I don't consider this cheating any more than using acids to dissolve matrix or surface blemishes.

Citric acid is a bit safer for several minerals (wouldn't try on fluorite, though) & I've used very dilute HCL for fluorite, but outside and not soaked the sample for very long.

All the warnings about strong or even diluted acids above are to be taken seriously & you should preferably know plenty about chemistry before considering handling acids & other hazardous substances. You can ruin your clothes or cause all kinds of nasty, dangerous situations, believe me. Been there, seen it, done it long ago & am perhaps lucky one is still alive & have almost an intact nervous system.

Cheers,

9th Dec 2016 02:03 UTCD. Peck

Nancy and others; If I "scared the bejesus" out of you, good. While that is not what I set out to do. I merely didn't want you, Nancy, to get hurt from some possibly bad advice to use an acid to clean your crystals (which you really didn't get).

I was trained as a chemist (first degree and some graduate). There is a lot of chemistry that I don't know, but I am well aware of the hazards of hydrofluoric acid, H₂F₂ . Even trained chemists are discouraged from using it unless they are specifically trained to do so. One of the insidious things about hydrofluoric acid is that one usually does not feel the burn for some time after exposure. Read the mortality tables. A splash the size of the palm of your hand, untreated for 90 minutes, and then given hospital treatment, can be deadly. Breathing the fumes for only a few moments can be deadly. I have not been apecifically trained in the use of H₂F₂ and I would not touch the stuff.

I know this is a rant, and for that I apologize. But if I have discouraged even one collector from using this deadly acid, I believe it is worth it.

9th Dec 2016 16:40 UTCNancy Gerlach

It wasn't just your post that scared the bejesus out me.. it was several others I read along with yours.. And I appreciate the warning because sometimes we (people in general) minimize the dangers of things even after being warned thinking the people telling us are dramatizing. I just wanted to write to say I HEARD you loud and clear. And I thank you for helping me stay safe during this adventure.

While I'm here- I was hoping to ask another question about a big Quartz crystal (30lbs). It's possible it's not even quartz- I'm pretty "mineral identity challenged" Anyway, I put it in Oxilic acid and it made it worse. So I've been soaking it in Iron Out and the yellowing is going away but the chalky white stuff in glommed on pretty hardcore.

9th Dec 2016 16:46 UTCNancy Gerlach

Thanks for the great idea about the diamond paste-- I'm going to give that a whirl and heartfully take your advice on the dangers of acids. I'm so grateful for the wisdom of the people contributing to this site. What an amazing resource for us nonscientific types.

Thanks again-

Nancy

9th Dec 2016 17:41 UTCThomas Lühr Expert

Nancy,

Your crystals look more like CALCITE to me, rather than quartz! In that case an acide treatment is the most worse you can do. ANY acid will do harm to calcite or even dissolve it.

Iron Out would be good INSTEAD of the oxalic acid, but it's too late now, unfortunately.

Thomas

10th Dec 2016 01:48 UTCD. Peck

Nancy, I would suggest that you switch for Iron Out permanently and stop using oxalic acid. If there is calcium in the water, oxalic acid is always going to give you that white film and it is almost impossible to get rid of. Iron Out removes iron stain and avoids a lot of problems. To remove calcite, use muriatic acid, but learn how to handle it first. HCl doesn't need to be feared, but it does need to be respected.

15th Dec 2016 17:27 UTCNancy Gerlach

Thank you - I will give it a go...

15th Dec 2016 18:52 UTCMatt Neuzil Expert

Joel, I am interested in these diamond pastes. Do you buy from chinese buyers? Is there a seller you prefer or suggest? I dont want to have any problems with the seller.

Matt

15th Dec 2016 20:12 UTCTravis Hetsler

Try Kingsely North, Neolithic Stone, The Jade Carver, or Dad's Rock Shop websites. Most of the pastes are made in China as are most of the diamond products available. You can also buy loose diamond powder and make your own pastes.

-travis

16th Dec 2016 05:48 UTCJoel Dyer

Hi Matt,

I got my pastes first from a Webshop in Finland, then realised that I could get most grit sizes directly from Ebay a bit cheaper.

I purchased the pastes from a UK shop advertising on Ebay UK, because I need to try and get stuff shipped from within the EU for shipping cost and tax reasons. You see, I can also get VAT off from most places, having a company registered for IT and now also mineral services :-).

Yes, Travis is right, of course: all of the products I've bought clearly are Chinese. Often some companies just re-label the syringes ;-)

I recently cleaned up a quartz crystal's surfaces (mica, iron oxides etc) for inspecting inclusions & inner structure through the rough surface.

Started with 5 micron & finished with 0.5 micron, using a toothbrush and cleaning the brush well between grit sizes with denatured alchohol. This did a much better job than acid and gave a not-unnatural-looking semi-gloss, in a very short time.

Below's a microscope picture of the sample, a not-so-good stack photo...

https://www.flickr.com/photos/finnchaga/30797611304/

Using 180-400(600) grit wet carborundum sandpapers, then diamond pastes variably from 40um to 0,25um, I have averted the need to buy an expensive flat lap polishing machine :-). Polished ore mineral sections for reflected microscopy need a very good polish.

Cheers,

16th Dec 2016 08:22 UTCThe Evje og Hornnes geomuseum, Fennefoss Expert

We also prefer the Waller solution, but don't use it without first testing a small sample.

I remember one day we thought Waller was safe to use on tumbled pieces of larvikite (a kind of monzonite), but to our great surprise and shock ALL the pieces were damaged!

Small holes were etched in each and every one of the pieces!

Even here the calcium in the feldspar turns out to be a problem!

Ron Werner

Norway

20th Dec 2016 02:49 UTCNancy Gerlach

Is this what you are talking about?

Which one would you buy from here? Sometimes I feel like I don't speak the same language as you experts.

http://www.shopwiz.com/shopping/search?q=diamond%20paste&gclid=CPDR4dXggdECFUeNfgodmcACqw

Peace!

Nancy

20th Dec 2016 03:23 UTCD. Peck

Hi Nancy,

I can't advise you about the diamond paste because I have never used it; but someone else will. Don't worry about "speaking the same language". That will come. We were all beginners at one time and the knowledge just kind of accumulates - - like moss on the proverbial rolling stone. Keep asking questions.

20th Dec 2016 06:02 UTCJoel Dyer

Hi Nancy,

Yes, the paste is sold in syringes (handiest), or more more regular use in small jars - cheaper then. Look at the seller's Satisfaction rating & even check some buyer feedback to see which place you should order from, considering the shipping costs and time also.

You should apply only very small amounts of the paste and indeed brush or clean off the specimen with denaturated alchohol or similar between each grit size, using perhaps also diluted detergent at the end. I apply a small tad of the stuff on copy paper & spread it a bit with my finger, also a very small amount on the sample. Then the stage-wise work begins :-)

Normally, for sawed specimens flats I use 40-20-10-5-2,5-1-0,5 and finally 0,25 micron. When "cleaning" specimens I wouldn't normally go higher than maybe 5 or so, becuase I might take away too much of the surface material & cause damage.

You will learn the techniques of what grits to use & how long to spend in each stage: you can often hear when you're getting close enough.

And indeed don't worry about "speaking the same language".

After 20+ years of spending time with my computer customers, I've learned to try and explain in plain language things to a widely varying audience matters that the computer dealers & impatient "nerds" unnecessarily speak of in incomprehensible gibberish.

Mindaters, especially the veterans, are good at guessing often what people mean & they're very good and generous at helping, so you will get the help you need, I'm sure :-)

Cheers,

Mindat.org is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization.
Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: May 10, 2024 21:06:12

Go to top of page