First evidence of CaCO₃-III and CaCO₃-IIIb high-pressure polymorphs of calcite: Authigenically formed in near surface sediments

Calcite is one of the most ubiquitous minerals in the Earth’s crust and is mostly present as calcite or the slightly denser polymorph aragonite. In addition five different phases of CaCO3 (calcite II-VI), which display similar structural features as calcite, have been observed with increasing pressure in different experiments by several authors. Experimentally, the CaCO3-III and CaCO3-IIIb polymorphs have recently been observed by Merlini et al....