strange experience!!! Big stones not so big!?

I did a liverflush last night and a couple of hours ago I past 3 big stones and several smaler ones. But when I cut the biggest one in half I found a grapfruit pice(the little bag that contain the juice), intact with the grapejuice still in there! The pice were right in the middle of the stone. Can some of the biggerstones be a product of several smallones gather together? Or HOW could it come it was inside the stone???

/Davva