Caryochroite, a Rare Mineral from the Titanosilicate Group: Crystal Structure, Crystal Chemistry, and Thermal Properties

Abstract

Abstract The crystal structure of the rare mineral caryochroite is determined for the first time using X-ray diffractometry and electron microdiffraction data. The new idealized crystal formula of the mineral is [Na(Sr0.5Ca0.5)Mg]3[Fe$$_{8}^{{3 + }}$$Mn($${\text{Fe}}_{{0.5}}^{{2 + }}{{\square }_{{0.5}}}$$)]10(Ti2Si12)O37(OH)14(Н2О)3. The parameters of the monoclinic unit cell refined by the least square method are a 16.550(3), b 5.281(2), c 24.25(3) Å, β 93.0°, Z = 2, space group P2/n. The crystal structure of caryochroite is a new type of Ti–Si lattice responsible for the large structural channels, which are able to enclose the exchange cations and a high amount of water components (OH groups and H2O molecules).