Pyrrhotite oxidation as an indicator of magma-air interaction during a volcanic eruption

Abstract

Pyrrhotite (Po) in the erupted materials from the Sakurajima Taisho eruption is sometimes oxidized to form magnetite (Mt) and hematite of ladder structure. The formation mechanisms were estimated based on previous Po oxidation experiments in air. Oxidation reaction of Po produces Mt and SO₂ gas that forms pores, resulting in the easy escape of SO₂ gas and easy access of O₂ gas to the Po-Mt interface, leading to the formation of a Mt column. Therefore, the ladder type products indicate the oxidation in the air.