Rock mineral (?) okimono

This okimono is about 2.75" long x 2.75" high x 2.25" wide, not signed or marked, weighs about 5 ounces. I am not sure what this is. I think it is some sort of stratum or mineral deposit in a rock that was turned into an okimono. I am not a rock hound so not really sure. I am also not sure if the shape in the center was carved and polished from the deposit or is as it was found. Also a very odd wooden base that was chipped away at until this rock fit into it. Very odd piece.

Purchased from Nagasaki, Japan, so assume it is Japanese. Also not sure what CW category it fits in as there is no Japan > Okimono category and we are now unlikely to get any more new categories....

This does not qualify as a suiseki, since it has been modified. I do not know if there is a category for pieces like this.

https://en.m.wikipedia.org/wiki/Suiseki

Probably falls under a general Japanese category, "interior stone".