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We were doing an experiment with vinegar and some fossils. We poured the vinegar on the fossils and they fizzed. In about an hour we saw whitish crystals, some were slightly rusty colored. We wondered what this was and what caused it.
Question Date: 2007-03-24
Answer 1:

What are you doing wrecking fossils?

Carbonates fizz when exposed to acid, and bicarbonates especially fizz. The acid liberates the carbonate ion, which then dissociates into carbon dioxide and water.The water remains liquid, but the carbon dioxide turns into gas.

The crystals are residue left behind. The red is probably hematite (rust). I don't know what the white is, likely quartz (silicon dioxide).


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