Hydroxyferroromeite, a new secondary weathering mineral from Oms, France

Abstract

Hydroxyferroroméite, ideally (Fe2þ+1.5□0.5)Sb5þ 2O6(OH), is a new secondary mineral from the Correc d’en Llinassos, Oms, Pyrénées-Orientales Department, France. Hydroxyferroroméite occurs as yellow to yellow-brown powdery boxwork replacements up to about 50mm across after tetrahedrite in a siderite–quartz matrix. No distinct crystals have been observed. The empirical formula (based on 7 (O þ OH) per formula unit, pfu) is (Fe2þ 1.07Cu2þ 0.50Zn0.03Sr0.03Ca0.01□0.36)S2(Sb5þ 1.88Si0.09 Al0.02As0.01)S2O6((OH)0.86O0.14). X-ray photoelectron spectroscopy was used to determine the valence states of Sb, Fe and Cu. Hydroxyferroroméite crystallises in the space group Fd3m with the pyrochlore structure and hence is a new Fe2þ-dominant member of the roméite group of the pyrochlore supergroup. It has the unit-cell parameters: a = 10.25(3) Å, V = 1077(6) Å3 and Z = 8. A model, based on bond-valence theory, for incorporation of the small Fe2þ cation into a displaced variant of the A site of the pyrochlore structure is proposed. Show more