marcasite

noun

1. (countable, uncountable)The orthorhombic form of iron disulfide, FeS₂, occurring as yellow crystals.
2. (countable, uncountable)Pyrite.
3. (countable, historical, uncountable)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.”