Worry stones, also know as palm stones or thumb stones are smooth polished gemstones. They have a thumb-sized indentation so you can carry it in your pocket and rub it for relaxation and stress relief. People use them by holding the stone between the index finger and thumb and rubbing one's thumb back and forth across the stone.
It is believed to be a self soothing exercise. The concept of worry stones is believed to originate in ancient Greece, Tibet, and Ireland. They were also popular with multiple Native American Tribes.