Beach:
Wikipedia gets it right in observing that beach glass is a strange
phenomenon — an odd case where something more valuable is created from
man-made litter. “Beach glass” is remnants of (usually coloured)
glass articles that have been broken and distributed in the sea,
carried and tumbled by time and tide, to the point where it is
smoothed, etched, and gently colourful.
Die-hard beach glass combers can identify the source of the glass by
colour. Blue is said to be pretty uncommon nowadays, as it came
from Noxema bottles — and Noxema has been distributed in plastic jars
for years already.
As littering and dumping are hopefully lessening, world wide, and fewer
products are available in glass containers, the availability of
“natural” beach glass should diminish in coming years.
This yields the delicate irony that lessening garbage in the ecosphere
is making beach glass a non-renewable resource.