No, it's all glass. Seaglass, fossicked from the shoreline where it's been thrown up by waves after being tossed, weathered, pitted by the leaching of its components by sea water. It comes in all colours with the rarest being red, made even more rare if it can be identified by the trace of a pattern.
Henry David Thoreau said, "The sea, vast and wild as it is, bears thus the waste and wrecks of human art to it's remotest shore....It lets nothing lie, not even the giant clams that cling to its bottom." So it is with seaglass, always flung back to where it came from.
These lovely pieces are by Lisa Hall and gives an idea of the colours to be found and treasured. It's almost like looking at priceless emerald, sapphire or jade. There are distinctions between the various seaglass specimens, antique seaglass develops a distinctive white residue resulting from extensive exposure to elements of the shoreline.
Seaglass comes from coastal regions everywhere especially it seems when strong storms coincide with a full moon.
New finds of old glass are becoming rare since we've taken to plastic bottles which only float and polute the beaches probably burying the seaglass underneath the dross. I hate to think how many times I've walked over a frosted piece thinking it was 'just old glass'.