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Techniques for CollectorsCleaning Dioptase

28th Jun 2011 07:36 UTCAnonymous User

Hello!

Report on cleaning Dioptase:

I tried to clean Dioptase crystal from a little matrix using a 30% HCl.

The Dioptase has melted and the solution is now full of a green gel...

-Kostas.

28th Jun 2011 10:17 UTCAlfredo Petrov Manager

Never use HCl on any copper silicates. Dilute nitric acid is OK on dioptase, if you just want to remove calcite matrix.

28th Jun 2011 11:33 UTCJolyon Ralph Founder

Always ask here before cleaning something in acid to avoid accidents like this. It's well known that dioptase decomposes in HCl

28th Jun 2011 15:11 UTCAnonymous User

Thank you all!

It was not an important piece,so Ihad no worries.

I just make sure I report,so that other members know that!

Thank you!~

28th Jun 2011 18:46 UTCDavid Von Bargen Manager

One of the old wet chemical tests was to put the unknown in HCl and see if a gel formed. It is fairly common for silicates to decompose.

30th Jun 2011 21:59 UTCMarc Maseman

When cleaning minerals, you should never use inorganic mineral acids (HCl, Sulfuric, Phosphoric, etc). Organic acids are typically much more user friendly. Based on what you are trying to remove, you can select the molecular size of the organic acid that will work on your particular mineral. Smaller molecules are more aggressive. Larger are less.

By organic and inorganic, I am not talking about organic in the sense of agriculture. In chemistry, we are are talking organic acids being ones that contain carbon. Inorganics contain no carbon.

Inorganics like HCL are one Hydrogen and one chloride. This is extremely volatile. An organic acid like citric acid is C6H8O7, which is obviously much, much larger and much less volatile.

From Wikipedia, some info on organic acids: Organic Acids on Wikipedia

Edit: No advertising please !

1st Jul 2011 01:14 UTCSteve Hardinger 🌟 Expert

Unless you are using **gaseous** HCl, HCl isn't volatile. Aqueous HCl is H3O+ Cl-.

And there are plenty of inorganics with carbon. Calcite, for one.

1st Jul 2011 10:13 UTCPeter Haas

"Smaller molecules are more aggressive."

This is bare nonsense.

1st Jul 2011 12:03 UTCRock Currier Expert

If you try to remove calcite from dioptase using acetic acid, for instance, you will ruin the dioptase. There may be organic acids that will remove the calcite without harming the dioptase, but why experiment around when you know a cheap acid like nitric will work fine. Also, some organic acids are generally more expensive than inorganic ones (perhaps citric acid excepted). Some times however you may need to resort to them. Like when you are trying to dissolve calcite from around fossil spiders that have been replaced by Celestite.

1st Jul 2011 15:09 UTCSteve Hardinger 🌟 Expert

Peter, I think the previous poster was confusing molecules with dogs.

6th Jul 2011 00:37 UTCAnonymous User

Hi!

Any species (not to say any specimen) needs a specific acid.Some species can be cleaned by more than one acid.

If a compound is organic,then it contains Carbon.The opposite is not true.

To my knowledge,when an acid or a base is a solid salt,the aqueous solution vapors is water.So Citric acid cannot be less volatile at room temperature.

Steve,HCl solution isn't volatile?What the vapor consists of?

6th Jul 2011 04:08 UTCPeter Haas

To my knowledge,when an acid or a base is a solid salt,the aqueous solution vapors is water

No. All components of the liquid phase are also contained in the gas phase (though at different concentrations). Even a ionogenic compound dissolved in water has a finite partial pressure in the gas phase above the solution, although this is exceedingly small. Anything else would be a violation of the second law.

So Citric acid cannot be less volatile at room temperature.

Less volatile than what ?

6th Jul 2011 15:26 UTCDavid Von Bargen Manager

From the MRDS sheet for hydrogen chloride.:

Vapor pressure at 25C is 190 mmHg

You don't really want to breathe the fumes - very bad for the lungs. I have had metal corroded that was in proximity to closed bottles of muriatic acid (screw top plastic jugs).

6th Jul 2011 16:56 UTCEvan Johnson

Repost, sorry.

6th Jul 2011 16:56 UTCEvan Johnson

For quite a few purposes I think discussing HCl vs. H3O+Cl- is pretty academic. I'll second the dangers of corrosion of various times that someone (and/or me) has left HCl solution uncovered or with poor ventilation. The incident that comes to mind was the grad student who intensely disliked the smell of pyridine and so left an open container of dilute HCl in cabinet under fume hood to neutralise. Fast forward a week or two, there was incredible, cave-like corrosion (which got worse with time despite attempts to reneutralise and cover with protectant).

EMJ

6th Jul 2011 23:44 UTCRoger Lang Manager

David Von Bargen Wrote:

-------------------------------------------------------

> From the MRDS sheet for hydrogen chloride.:

> Vapor pressure at 25C is 190 mmHg

>

> You don't really want to breathe the fumes - very

> bad for the lungs. I have had metal corroded that

> was in proximity to closed bottles of muriatic

> acid (screw top plastic jugs).

You should see my bathroom .. i once forgot a small open container with 10 % HCl and left for 2 weeks ... meanwhile the water evaporated and the concentration of HCl reached the "smoking" conc besides the "normal" HCl evaporation.. my metal fittings are a wreck now ;-) and the atmosphere was at least hostile when i came back. Fortunately i had closed the bathroom door.

7th Jul 2011 03:46 UTCAnonymous User

Hello!

Peter,thank you for correcting me.I've asked this question so many times and I always get a different answer.

Less went as an answer to the previous post claiming that Citric acid is less volatile than HCl and other acids.

Both solutions of Citric and HCl have odor (practically when I open the container,so I should have guessed that vapors are not just water (Citric).

Keep chemicals outside the house at a well protected places and the containers sealed as well.Animal and people can be harmed.

I've seen nervous system disorders due to working at chemical stores and all the bottles were closed.Keep all safety rules and ask here about them.

Everyone is asking about minerals and I only once saw a post about safety.

I remind everyone that NOT in all countries concentrated compounds are illegal and they are easy to buy.

I have a friend who had half his hand tissues necrotic after he tried to clean a specimen with Hydrofluoric and the glove was pierced.The doctors didn't know how to react and they didn't provide any Calcium medicament.I'm sure in the future he will face internal organ failure.Thankfully he's still alive.

I recommend that someone writes down an article about safety and it will be always visible for users of this forum.

-Kostas.

16th Jan 2014 17:49 UTCMolly Gove

I am not a chemist and am unfamiliar with acids. I have a piece that has dioptase crystals embedded in something else. There is some rust that is increasing and occluding the crystals.

What is a safe and accessible way to clean the rust off without hurting the crystals?

Thank you!

17th Jan 2014 12:59 UTCRock Currier Expert

Molly,

Could you give us a picture of the dioptase you hope to clean?

17th Jan 2014 21:28 UTCMolly Gove

here is a photo... there is more rust now...

is there anything you know of to clean that will not hurt the dioptase crystals?

17th Jan 2014 21:38 UTCMolly Gove

there is more rust now than when this photo was taken.

do you know of something that is sort of easy to get for a lay-person to clean with that will not hurt the dioptase crystals, but will remove the rust?

17th Jan 2014 21:54 UTCRock Currier Expert

Iron out should not hurt the specimen, but still, if you are worried about using it, take a tiny fragment from the specimen, preferably one having a tiny bit of dioptase and some of the brown material and try it out on that first and watch what happens. When working with minerals it is usually a good idea to try it out on an inferior specimen rather than the good one first, unless of course you have cleaned other specimens from the same locality before.

17th Jan 2014 22:10 UTCSteve Hardinger 🌟 Expert

In some cases, the brown is more than just a thin coating of "rust"; instead it's thick, and is holding the dioptase crystals in place. So ask yourself would it be better to remove the brown and maybe lose some (or all) of the dioptase crystals from the sample, or will it look better as it is, with more dioptase? Personally I am fond of the deep green/brown contrast. Looks very earthy.

17th Feb 2014 01:49 UTCBarry Miller

Molly Gove Wrote:

-------------------------------------------------------

> there is more rust now than when this photo was

> taken.

>

> do you know of something that is sort of easy to

> get for a lay-person to clean with that will not

> hurt the dioptase crystals, but will remove the

> rust?

>

I don't understand - why is the rusty colored material increasing? Anyone know?

17th Feb 2014 17:00 UTCDoug Daniels

I too am confused as to how the "rust" is increasing. I also agree with Steve - it looks like, if you dissolve away the rust, you may have a number of nice, single, micro crystals of dioptase, and not a matrix specimen. I'd leave the thing as-is.

24th Feb 2014 23:11 UTCRoger Lang Manager

Try with ultrasonic first*. The reddish stuff looks like an iron-bearing clay which wouldn´t be removed by acids. I achieved quite good results on Omaue and Kaokoveld dioptase with a hi-pressure water gun and with ultrasonic.

Acids were quite bad - even nitric which should spare the dioptase but may produce unpleasant yellowish and otherwise unnatural colours if not rinsed thoroughly.

Molly your specimens looks like Kaokoveld (either Omaue or one of the neighboring occurrences) .. i dealt with them and if the matrix is clayey - don´t do anything* .. the specimen doesn´t look that bad as you posted it.

Cheers

Roger

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