Worry stones are crystals/stones that have been polished and a slight indentation carved into one side.  They are great to carry in your pocket and you can rub your thumb in the indentation to help with worry, stress, or similarly to how you'd use a fidget spinner.
 
Listing is for 1 worry stone.  I will intuitively choose they type unless you put a comment in when ordering requesting a specific type of stone.