marcasite

noun3

1. •
   The orthorhombic form of iron disulfide, FeS₂, occurring as yellow crystals.
2. •
   Pyrite.
3. •
   (historical) Any of various metal sulfides, usually iron sulfide minerals.

   • If he wants to speak as a physician, however, he must say, this marcasite is the man's disease, hence it will cure him. — 1999