which stones sink?

I did my 5th flush the other day. I know I passed a whole bunch of stones on two occassions as I felt them, it was unmistakeable, but all of them sank to the bottom. So therefore I have no idea of what they looked like or exactly how many.

Is it true that some stones sink? I have read many posts that seem to agree that only the calcified stones sink. However,I once passed a whole bunch of stones on my first flush, almost white in colour, which I thought were calcified only they floated so I'm slightly confused about which stones sink and which ones don't? And if these white stones weren't calcified what were they?

Can anyone please clarify?

Many thanks :)