Petoskey stone
 
This is  a rock and a fossil, often pebble-shaped, that is composed of a fossilized rugose coral, Hexagonaria percarinata. Petoskey Stone is a type of hexagonaria fossil that dates to around 350 million years ago, and were originally a type of coral.
 
An "Eye" formation helps with opening the third eye. Prevents mischievous spirits  from hindering proper communication with those on the other side.Stimulates mystical abilities. Stimulates intuition and can be used to help with meditation.