Pyrite

The mineral pyrite, or iron pyrite, also known as fool's gold, is an iron sulfide.  Pyrite is considered the most common of the sulfide minerals. Pyrite's metallic luster and pale brass-yellow hue give it a superficial resemblance to gold, hence the well-known nickname of fool's gold.  Pyrite is rated between 6 and 6.5 on the Mohs hardness scale.  Pyrite is thought to encourage self-recognition, as well as reveal secrets and memories.