Crystallographic analysis of phase transformations in danburite CaSi₂B₂O₈

The crystallographic analysis of the structures of danburite CaSi₂B₂O₈, which is orthorhombic (Pnma) at normal pressure, triclinic (P1 ¯) at a pressure of 25.4 GPa, and monoclinic (P2₁/c) at a pressure of 32.3 GPa, shows that they are based on a joint packing of Ca cations and O anions whose regularity increases with pressure. A common structural fragment is the configuration of atoms related by the glide reflection plane retaining for Ca and a part of O, B positions with a possible Si migration according to the seesaw mechanism (N. V. Belov).