The Ancient Incans, Greeks and Egyptians all valued marcasite. It was not uncommon to see Cleopatra herself adorned in Marcasite gemstones.
Marcasite is a natural gemstone and is derived from a mineral called 'pyrite'. Pyrite and Marcasite (FeS2) are iron disulfide compounds, however Marcasite jewelry is made from Pyrite (fool's gold), not, as the name suggests, from Marcasite. Pyrite is similar to Marcasite, but more stable and less brittle.
Pyrite works with the solar plexus, increasing one’s vitality. It provides a massive boost to one’s willpower and directs this energy towards overcoming bad habits, allowing one to build a strong foundation for new healthy patterns, and a constant flow of positive energy.