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Techniques for Collectorsdissolving rhodochrosite

14th May 2007 07:38 UTCAlbert Russ Expert

I have the following problem,. I obtained a very nice rhodochrosite from Peru, but it contains some damaged crystals on sides. I decided to remove them completely while preserving the undamaged crystals. I covered the undamaged crystals with wax and tried to dissolve the undesirable ones with HNO3. However, it does not seem to dissolve them, or at least I can see virtually no bubbles forming. What would you reccomend me on using? It seems that Calcium carbonate dissolves in acid much faster than manganese carbonate. Any experience with this? Thank you.

14th May 2007 10:28 UTCKarel Bal

Hi Albert,

Rhodochrosite is dissolvable in warm HCL.

Kindest regards.

18th May 2007 13:19 UTCAnonymous User

Hi all!

I recomment removing them mechanically,finding the limits of the brocken crystals and breaking them just where the contct is.HCL may destroy the rest of the crystals!Polishing the side crystals would give a pleasant look to the specimen as well,no need to remove them!

Hope I helped!

-Kostas.

19th May 2007 05:33 UTCDon Saathoff Expert

Waxing and HCL should work, but you're taking a BIG risk.....Konstinos' suggestion fits MUCH better

8th Jun 2007 11:41 UTCRock Currier Expert

Albert,

Try mechanical means rather than chemical. Rhodochrosites and siderites are both carbonates but you will play merry hell trying to use acids to dissolve any quantity of them. If you take rhodochrosite and siderite and grind them to a fine powder and put a drop of a hot strong acid on them, you will get some bubbles, but not anything like the fizzing you will get if you put a drop of those acids on calcite. I had a nice specimen with siderite? growing on cassiterite and quartz from Bolivia. I finally did manage to dissolve the siderite but had to use almost boiling acid over an extended period of time to do it. The first big and fine rhodochrosite that came out of Peru from Pasto Bueno was sold to Gary Nagen by a young mine geologist for less than $50. He told me that he knew it was not rhodochrosite because he put a drop of hydrochloric acid on it and it did not bubble. I had not the heart to tell him that it really was rhodochrosite and that Gary sold it for more than he was likely to make in his life time.

Rock

20th Sep 2007 19:44 UTCKevin Xu

what's the full spelling of HCL?thanks

20th Sep 2007 21:04 UTCPaul L. Boyer

Rock has it in his post. HCl is the chemical shorthand for hydrochloric acid, since its composition is one hydrogen and one chlorine.

20th Sep 2007 22:03 UTCKevin Xu

thanks Paul,I would like to know HCL also.

20th Sep 2007 22:24 UTCPaul L. Boyer

I am not sure what you mean. Technically, the "L" should not have been capitalized. When they say "HCL" they really do mean "HCl", the acid. Sometimes you can get it labeled as muratic acid in hardware stores. It is used as a cleaner for masonry, etc. While listed as muratic acid, it is hydrochloric acid.

20th Sep 2007 22:28 UTCKevin Xu

ok,gotcha,thanks again

20th Sep 2007 23:59 UTCPaul L. Boyer

Just realized I forgot an "i". It should be "muriatic acid". Sorry about that.

21st Sep 2007 11:06 UTCPeter Haas

"While listed as muratic acid, it is hydrochloric acid."

In the strict sense, "hydrochloric acid" refers to pure HCl (a gas), and "muriatic acid" to its aqueous solution.

21st Sep 2007 14:32 UTCDonald Vaughn

not really hydrogen chloride is the gas. an acid must be in a solution; water or otherwise to allow for icreased cations

21st Sep 2007 15:40 UTCChristian Bracke Expert

Maybe you try ascorbic acid (pure vitamin c) in a solution in water, I remove Mn-oxides with this, should dissolve rhodo´s as well (may take some time).

Christian

21st Sep 2007 16:00 UTCSteve Hardinger 🌟 Expert

I see too many chemical errors here in Mindat discussions, and this one really cleaves my crystal. So let me clarify a few issues.

Pure, anhydrous (no water) HCl (not HCL) is a gas, correctly named "hydrogen chloride." Hydrogen chloride has a hydrogen atom, and therefore can be an acid. A substance does not have to be dissolved in water (or any other solvent) to have acidic proerties. When hydrogen chloride is dissolved in water, the resulting solution consists of water, hydronium ion (H3O+) and chloride ion (Cl-). No significant amount of HCl remains. This water solution of hydrogen chloride is called "hydrochloric acid". Industrial-grade hydrochloric acid is called "muriatic acid". Muriatic acid is often yellow due to impurities. For mineral cleaning purposes, muriatic acid and hydrochloric acid can be used interchangably, although the former is usually much less expensive.

Quiz tomorrow. Class dismissed.

Steve Hardinger

Professor of Chemistry, UCLA

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