Some stones have a little room inside them. A pocket of tiny crystals, a clear patch where the polish lets you look down into the stone, a vein that cuts straight across. These are the ones I keep picking back up.
The big white stone at the top has a window of tiny crystals along its upper edge and fine banding around the rim.
Blue-gray with one black vein running straight through it, like somebody drew it on.
A gray stone with a pocket of tiny crystals. Turn it a little and the pocket catches the light differently every time.
Frosty crystals on one face, smooth and clear on the other.
I could look into any of these for a while.