The TS-block (Titanium-Silicate) is the main structural unit for the seidozerite-supergroup minerals.It consists of a central O (Octahedral) and two adjacent H (Heteropolyhedral) sheets where Si 2 O 7 groups occur.Cations in each sheet of the TS block are arranged as a closepacked layer forming an ABC close-packing.The fifty-two TS-block minerals are divided into four groups, based on the content and stereochemistry of Ti (+ Nb + Zr + Fe 3+ + Mg + Mn) and topology defined by the linkage of H and O sheets.In rinkite, bafertisite, lamprophyllite and murmanite groups, Ti (+ Nb + Zr + Fe 3+ + Mg + Mn) equals 1, 2, 3 and 4 apfu.In the crystal structures of TS-block minerals, TS blocks either link directly or alternate with I (Intermediate) blocks.As a dominant cation at a specific site, 6 Ti is substituted by Nb 5+ (12 minerals), Zr 4+ (2 minerals), Mg 2+ (2 minerals), Mn 2+ (1 mineral) and Fe 3+ (1 mineral).The crystal chemistry of Nb 5+ has been considered in the rinkite, bafertisite and lamprophyllite groups where Nb 5+ occurs as a dominant cation at the M O 1 site in the O sheet or at the M H site in the H sheet. Nb-dominant mineral species do not occur in the murmanite group.The different types of linkages in minerals with the TS block are a result of the bond-valence requirements of anions X O M and X O A shared by the O and H sheets, excluding the anions of the Si 2 O 7 group.The stereochemistry of the 4-coordinated X O M anion in the O sheet, which is a bridge anion for the M H cation in the H sheet and three M O cations in the O sheet, has been considered.New developments, such as existence of counterpart structures in lamprophyllite and murmanite groups and successful prediction of three new minerals, have been reported.
Соколова et al. (Fri,) studied this question.