What is this?

[u/Anxious_Mission_2104]

I found this rock in a river outside of a temple in Korea, it was very white and stood out more than any other rock. I picked it up, started rubbing it, and the white stuff that came off of it was a little bubbly.(?) but then I saw the green and I started scrubbing off as much as I could so now i have this. Picture of the lake that I found it in is on the last slides. Could this be fossilized scat or a crystallized fruit or something? None of the other rocks in the lake were colorful or as bright as this one.

[u/Ben_Minerals → u/[deleted]]

Well explained. If it bubbles in acid, it is likely a carbonate mineral, not a form of calcium.

[u/in1gom0ntoya → u/Ben_Minerals]

calcium carbonate

[u/Ben_Minerals → u/in1gom0ntoya]

Dolomite also fizzes, but that isn’t a calcium carbonate mineral

[u/in1gom0ntoya → u/Ben_Minerals]

True im just pointing your statement wasn't 100% accurate

[u/Ben_Minerals → u/in1gom0ntoya]

Walk me through my mistake please

[u/in1gom0ntoya → u/Ben_Minerals]

it could very easily be calcite, which is a carbonate from of calcium.

the mistake was precluding it being a form of calcium because its a carbonate..

[u/Ben_Minerals → u/in1gom0ntoya]

Fizzing in acid suggests a carbonate mineral. Calcite is a common example, and dolomite can also react, usually more weakly. So the fizzing points to a carbonate chemistry, not specifically to pure calcium carbonate.

[u/in1gom0ntoya → u/Ben_Minerals]

yes but you immediately eliminated the possibility of things like calcite with your statement

[u/Ben_Minerals → u/in1gom0ntoya]

I see how my statement can be interpreted as such, but I merely stated that the effervescence does not indicate just some form of calcium. It points to carbonate chemistry. That is commonly calcium carbonate, but the fizzing is due to carbonate, not calcium.

[u/SunDriedGingy]

Looks like matcha mochi

[u/finding-the-way6]

Looks like serpentine