This is the Wiki definition of Sea Glass;

Sea glass is glass found on beaches along oceans, bays, rivers, gullies or large lakes that has been tumbled and smoothed by the waves, water and sand, creating smooth, frosted shards of glass.

Sea glass collecting has become a hobby. It cant be bad when you have to visit the beach to stock up on materials.

The feeling inside when you find a perfectly tumbled piece of sea glass glinting, partially hidden in the sand and pebbles, is one of life's simple pleasures.