a reddish-brown, soft, brittle, cubic mineral, copper iron sulfide, CuFeS, an ore of copper that tarnishes to a dark purplish color when it is fractured
See bornite in American Heritage Dictionary 4
(bôrˈnītˌ)
noun
A brownish-bronze, lustrous copper ore with the composition Cu5FeS4 that tarnishes to purple when exposed to air.