GeologyRocks

I'm not sure what you mean, but could it be a strange flowstone deposit?

http://en.wikipedia.org/wiki/Flowstone

If you have a picture that would help.

I checked the wiki page, thanks. But sometimes there're problems to use wikipedia in China. I need further explaination. Some say popcorn is formed because the CaCO3 is deposited onto the sands under the Ca(HCO3)2 water, similar to cave pearls, and I got a picture here.

Some say is because of capillarity, and here is a pic which I took from the book "Geology".

OK maybe they're different popcorns, but I'm not sure how are they formed. Wanna know the exact story of its formation.

I'm interested in karst caves recently...

It aint what you are looking for but there is some other kind of rocks that are like popcorn, too. off the west coast of some central american country you can gather rocks on the 3000m deep seafloor. if you bring them up to the surface they start "exploding" with loud pop-pop-pop sounds.

Thanks. I searched on net and read many relational articles, and have got some clue. The popcorn shaped stones can be formed in several ways. Some under water as deposition onto sands, some caused by seeping solution of Ca2CO3. Ha I know the "poping" stone, maybe called montmorillonite...