This stone was found in an area of Germany where there are many glacial stones scattered across the landscape. This one was different, however, because it has what I would call "filaments" inside. You can see them throughout, and there is a visible center full of them.
I have several others all from the same area as well, and they greatly vary in appearance. A few have natural holes in them, are pocked, clearly are glacial stones or some that also look like amber.