The heterophyllosicate polysomatic series

By analogy with phyllosilicates, a group of titanium silicates whose structures are based on TOT-like layers have been called heterophyllosilicates (Ferraris et al. 1997). In these structures, rows of Ti(Nb)-octahedra (hereafter, Ti-octahedra) are introduced in a T sheet along the direction which is parallel to a pyroxene tetrahedral chain (Fig. 17). HOH layers are thus obtained where H stands for hetero to indicate the presence of the Ti-octahedra in a sheet corresponding to the T sheet of the layer silicates. Because the edges of the Ti-octahedra and Si-tetrahedra have close lengths dimensions, the insertion of the octahedra in a T sheet does not produce strain. As summarized by Ferraris (1997), three types of HOH layers (Fig. 18) are known so far. 

Bafeisi6-like ( HOH)s layer. A bafertisite module i , /2T4[Ti2(0)4Si40i4](0,0H)2, is one-to-one intercalated with a one-chain-wide mica-like module 

/r3[Si40io](0,OH)2 (/ and Y represent interlayer cations and octahedral cations, respectively). 

Astpllit-like ( HOHI layer. With respect to the bafertisite-like layer, a second one-chain-wide mica-like module M is present between two bafertisite-like modules. 

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