Ferric sulphide, pyrite, FeS2, occurs native in large quantities.
"An Introduction to Chemical Science"
R.P. Williams
She lay on silken cushions, upon a throne artfully fashioned from a huge pyrite-crystal, and some maidens were assiduously chafing her tender limbs, which seemed a rare union of milk and purple.
"Henry of Ofterdingen: A Romance."
Friedrich von Hardenberg
It requires the mining of pyrite and sulphur.
"The Economic Aspect of Geology"
C. K. Leith