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Andrew Alden

Giving Fossils the Acid Treatment

By June 17, 2013

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acid treatmentWhen I was given a grab-bag of rock specimens the other week, this piece of limestone studded with little Devonian corals caught my eye. A few quick tests told me I could try acid digestion on it, so that's what I did. See the process, the results and the trade-offs after I bathed it in hydrochloric acid.

Related:
The acid test
Oxalic acid treatment of minerals
Fossil collecting tools
Non-fossils
Thamnopora coral specimen — Geology Guide photo

Comments

June 17, 2013 at 4:45 pm
(1) David Phillips says:

and now you have crumbs vs a nice specimen that could have been cleaned other ways

June 17, 2013 at 10:28 pm
(2) Geology Guide says:

That’s true. Sometimes you want a specimen, other times you want the crumbs. I did the experiment to show both possibilities.

June 18, 2013 at 12:08 pm
(3) Eric Logan says:

I recently used concentrated hydrochloric acid to dissolve part of a dark-grey colored, whitish veined limestone rock (common locally). The undissolved core showed some whitish quartz in layers and spongy masses, and also a lot of dull black material. I haven’t tested it, but is it plausible that the black stuff is carbon or hydrocarbon? I previously treated similar limestone with HCl and observed black-colored bits suspended in the effervescence.
Thanks;
JEL

June 18, 2013 at 8:08 pm
(4) Geology Guide says:

It’s plausible, and easy to test by trying to ignite the black stuff.

June 29, 2013 at 5:04 pm
(5) Michael says:

I have some rock with euhedral celestine in calcite matrix. It mostly looks like a big blue and white mess (respectively). I once tried dissolving a small part of it with HCl and it did reveal the beautiful celestine crystals. Maybe I should take one of the larger specimens with larger crystals and give it the HCl bath.

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