Cleaning with Muriatic Acid

[PennyG]

Good afternoon.
I have a lot of pyrite specimens I have collected over the years and want to clean them.
I've read up on the cleaning process by using Muriatic Acid, however, some say to dilute in 2 parts water/ 1 part Acid, and then some articles say not to dilute.
Any words of advice would greatly be appreciated.
Thanks [emoji4]

 

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[JasonG]

Depends on the concentration the article is talking about and the concentration of the HCl (muriatic) that you own. The article should mention it someplace and your bottle will have it listed on it.

If you leave specimens to soak just make sure that the acid doesn't react with or dissolve accessory minerals. Stuff like hematite won't really give a visible reaction but it'll be dissolved when you check on it the next morning, I use it to dissolve iron oxides out of gold nuggets.

 

[PennyG]

Thank you. Here are a few I'm thinking of using in the Acid.
1)

2)

3)

4)

5)

6)

7)

8)

I found all of them except for number four on the beach of Lake Michigan , Illinois side.
Number four I brought back from Crater of Diamonds.
Pic 8 just a few random smaller ones.

 

[PennyG]

Tried to enhance 8 so perhaps it gives a better look with out a bunch of individual pics. Not sure it did much .

 

[PennyG]

Spec one still has a lot of iron I suppose. It's hard to show but there is still a lot of I'm guessing iron around it. I tried zooming in and showing the details on that one as well but no luck . The pyrite has the cubed look but very tiny.

 

[JasonG]

Interesting, are those pyritized corals in #2 and #3?

The HCl will dissolve those iron oxides (rust) off slowly if you are soaking them, not sure if that's what you are going for or not. Also any carbonates, those will fizz like crazy though so you'll see it right away.

 

[PennyG]

Yes , I believe it is pyritized coral. The specimen in number two looks silver in some area and pyrite in other areas.
Yes , the iron oxides is what I'd like to remove.

 

[JasonG]

The first pic of specimen #2 also looks like 3 fingers holding the pyritized portion and carved greek style out of marble or something...pretty cool.

Anyways, I can't tell what type of rock they are and you've probably already considered this, but fossils commonly form in limestone, which is a carbonate, and it will readily react with the acid. Just a heads up. Probably a good idea to err on the side of lighter concentrations and start off slow when you begin to clean them.

And the requisite warning: wear nitrile gloves and do it in a well ventilated area or outside, that stuff burns your nasal passages if you accidentally breathe it in (first hand experience).

 

[PennyG]

The first pic of specimen #2 also looks like 3 fingers holding the pyritized portion and carved greek style out of marble or something...pretty cool.

Anyways, I can't tell what type of rock they are and you've probably already considered this, but fossils commonly form in limestone, which is a carbonate, and it will readily react with the acid. Just a heads up. Probably a good idea to err on the side of lighter concentrations and start off slow when you begin to clean them.

And the requisite warning: wear nitrile gloves and do it in a well ventilated area or outside, that stuff burns your nasal passages if you accidentally breathe it in (first hand experience).

Thank you for all you help. I might not put 2 &3 in the acid bath.
You've been a huge help.

 

[PennyG]

I'm beginning to think this one rock is not pyrite.





It's coloring is actually silver

 

[JasonG]

Hard to tell from a picture but it kinda looks like pyrite.

Could do a streak test. Or the scratch 'n sniff, pyrite smells pretty sulfer-y when you scratch it. Same with hitting it with a blowtorch, rotten eggs. I hate to advise anything destructive though.

*I don't know enough about chemistry to know you won't create H2S gas either (very dangerous) if you start mixing heat with sulfur and hydrogen compounds come to think of it, so ignore that.

 

[PennyG]

The scratch test was a dark black line.

 

[JasonG]

Hmm yeah, silvery mineral streaking black, likely to be pyrite as we originally suspected. Best of luck with the cleaning, I'm off to the mountains to prospect for the weekend!

 

[Capt Nemo]

Don't use on the fossil coral! Some of those are limestone/dolomite. We have a lot of iron mixed with the limestone around here. Some seems to possibly be meteorite fragments, as they're spherical. At least that's what I found in one sample I dissolved in HCl.

 

[Eu_citzen]

For pyrite I very much prefer citric acid. A milder, more fool proof alternative. Though: Do not use on fossils or carbonates! (unless its them you wanna remove)

To prepare: simply add as much citric acid as water will dissolve and then use that for the pyrite.

Citric acid is usually available at the food store.

 

[PennyG]

Thank y'all very much for the good info. Sorta got side tracked but getting back at it today.

 

[PennyG]

Looking a tad bit better and more like pyrite.

 

[hvacker]

You got me thinking about trying the product, CLR. It's in the grocery store.
Says it stands for calcium, lime, and rust. I think I'll give it a try.
Mostly thinking about the rust.

 

[JasonG]

You got me thinking about trying the product, CLR.
Mostly thinking about the rust.

CLR does work. Dunno why I didn't think to mention it too. It's much slower, but also safer.

 

[hvacker]

CLR does work. Dunno why I didn't think to mention it too. It's much slower, but also safer.

Ya, I'm a American and want instant results too. I guess I could slow down a bit and smell the roses.
I'll give it a try this weekend. There must be a rock out in my yard somewhere. I'll let ya know.
If memory serves along with HCL there are other acids in the bottle that attack rust better than HCL.