Magnetite-like nanocrystals formed by laser-driven shocks in siderite

Laser-driven shock experiments were carried out on Mn and Mg-bearing natural crystalline siderite under vacuum. Raman spectroscopy and transmission electron microscopy were performed on samples recovered from shock pressures between 8.4 GPa and 25.9 GPa. Two different iron oxides were observed in the laser impact crater: hematite – already present in the starting sample – and a spinel-structured phase, both associated with iron carbonates. This nanometer-sized Mn-bearing magnetite-like phase results from shock-induced decarbonation of siderite. High-pressure shocks, such as meteorite impacts, are a plausible mechanism for generating nanocrystals of magnetite from Fe-carbonate-bearing terrestrial and extraterrestrial materials.