# What is the oxidation state of copper and iron in chalcopyrite?

What is the oxidation state of Cu and Fe in chalcopyrite ($\ce{CuFeS2}$)? Some websites tell that it is $\ce{Cu(I)Fe(III)S2}$, and others tell that it is $\ce{Cu(II)Fe(II)S2}$. Which is right?

A number of papers report that the formal valency states of chalcopyrite are best considered as $\ce{Cu+Fe^3+S2}$, based on various computational and spectroscopic evidence.