Abstract
Arsenian pyrite is the main mineral host of gold in Earth's largest deposits, as well as a major phase contributing to arsenic in the environment. Here we report the discovery of a new form of arsenian pyrite in which As 3+ substitutes for Fe (Fe,As)S 2 (here called As 3+-pyrite), in contrast to the expected substitution of As 1-for S (here called As 1-pyrite). Unlike typical As 1-pyrite, As 3+-pyrite exhibits a linear anti-correlation between As and Fe...