Is it always a shattered bit with a knife-like edge?
No, I don’t think so…
On the beach, I used to find bits of glass so soft and rounded that I didn’t believe they were glass. They were jewels. The blue ones were rare and expensive Tiffany sapphires. Clear became diamonds. Green were emeralds. Even the commonplace brown became amber.
I didn’t know where these jewels came from. I didn’t connect them to the glass slipping out of my small hands and—whoops–breaking on the kitchen floor to the soft jewels in my sandy palm. I didn’t know the amber and emeralds came from too many Pabst Blue Ribbon Beers or Molson Ales on the rolling seas. Or that my precious sapphires came from milk of magnesia bottles meant to settle a sea-sick stomach. I didn’t know how the ocean lurched and leaned and made bottles slips from wet hands, then tumbled the bits across the ocean floor, smoothing the sharp edges until they wash up in grains of sugar dust sand buried like treasure.
In the winter, I pour the treasure on my bed and put one of the gems in my mouth so I can taste the salt and the sun and the ocean.
A shard of memory.

The practice is inspired by Naomi Shihab Nye and her notion that words are like oars. Dip them in the water. Explore with them. Feel how they touch and bump up against one another. Let them take us further down the stream.