Charlevoix stone or Favosite Coral

 This colony coral is composed of marine animals which are polygonal to slightly rounded in shape. The closely adjoined colonies give the formation a honeycomb-like appearance. Found associated with the Petoskey Stone of the Lower Peninsula of Michigan, these Favosites lived in shallow water reefs and shales. Commonly found on beaches or in gravel quarries from Petoskey to Traverse City. Hardness is from 4 to 5.