Tried vinegar on a weird rock from the creek and it totally fizzed

Honestly, I was just messing around with some stuff I found in the creek behind my place. I had this one lumpy, kinda yellowish rock that felt really light. I remembered something about using vinegar to test for calcite, so I grabbed the plain white vinegar from my kitchen. I put a few drops right on it and it started fizzing like crazy, like a soda. I wasn't expecting that much of a reaction at all. It went on for a good 30 seconds. I looked it up and learned that it means the rock has carbonate minerals in it, which makes sense for the area. Now I keep a little bottle of vinegar in my field kit just for quick tests. Has anyone else had a rock react way more than you thought it would? What did you find out it was?

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ruby6596mo ago

Tbh that's a really cool find. Did you try to scratch the rock with a coin or a knife before the vinegar test? I'm wondering if you could tell how hard it was, because sometimes that fizz can mean different things. Like, if it's soft enough to scratch, it might be something like chalk or a really pure limestone. If it's harder, it could be a different carbonate rock.

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morganmartinez6mo ago

Oh man, I feel called out. I just dumped vinegar on it like a kid making a volcano. Didn't even think to scratch it first, @ruby659. My rock ID process is basically "ooh shiny" then "will it fizz." Probably why my collection is just a box of weird-looking gravel.

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beth_park6mo ago

Actually, vinegar fizzing always means carbonate minerals are present, no matter the rock's hardness. The scratch test just helps figure out which specific one it is.

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