Ferroan monticellite in serpentinites from the Happo ultramafic complex

Abstract

Ferroan monticellite (or magnesian kirschsteinite) occurs in the Happo ultramafic complex, central Japan. The ferroan monticellite has irregular shapes and replaces primary olivine in serpentinized peridotites. The ferroan monticellite is different from previously reported monticellite compositions in high Fe and Mn contents. Observed textures suggest the coexistence of the ferroan monticellite with antigorite ± diopside. Thermodynamic calculations show that the assemblage is stable at a low-temperature, and low SiO₂ and high Ca²⁺/(H⁺)² activities.