Driftglass," I said. "You know all the Coca-Cola bottles and cut-crystal punch bowls and industrial silicon slag that goes into the sea?"

I know the Coca-Cola bottles."

They break, and the tide pulls the pieces back and forth over the sandy bottom, wearing the edges, changing their shape. Sometimes chemicals in the glass react with chemicals in the ocean to change the color. Sometimes veins work their way through in patterns like snowflakes, regular and geometric; others, irregular and angled like coral. When the pieces dry, they're milky. Put them in water and they become transparent again.

Author: Samuel R. Delany