Is it "Cooked"?
In this video I talk a bit about the process of 'hydration', the term used for the chemical transformation that glass undergoes in bodies of water where the Ph is higher than 7. This includes all of the oceans of the world, as well as a couple of the Great Lakes here in North America.
If the Ph in the water is above 7, then the soda and lime will be, over time, drawn to the surface of the glass, causing the silica part of the structure, or the glass, to break free from the structure. So, what we are left with, on the surface of the structure, are the bonding agents of soda and lime....this helps to explain why the texture of sea glass is so different from glass as we know it, or even glass that has been tumbled in a machine.
This also helps to explain why machine-tumbled glass can never duplicate the texture of naturally refined sea glass....machines work from the outside-in, whereas sea glass is, on a molecular scale, coming apart from the inside-out. Machines are changing the structures physically, and sea glass is predominantly changed chemically. That just takes time, and time is the one factor that is impossible to replace and impossible for machines to duplicate.