1.5" x 1.5" piece of grey agate with a art deco style bronze bezel
 
ALSO AVAILABLE AS A NECKLACE ON STERLING SILVER
 
Another great look is on a leather cord/necklace.
 
Agate Healing Properties:  Cleanses and stabilises the aura, eliminating and transforming negativity.  It enhances mental function, improves concentration and perception. It soothes and calms and creates a sense of security and safety.