Crystallochemical classification of sulfates

Crystal Chemistry of High-Temperature Borates

“…Each subsequent classification is, as a rule, superior to the previous one. The schemes proposed by 1966 were thoroughly and critically discussed in the review [91]. Therefore, there is a sense in dwelling shortly on some of them here.…”

“…The crystallochemical classification of borates suggested in [91] is based on two main characteristics: the structure of boron-oxygen polyanions and the manner in which they are combined. It also takes into account the peculiarities of the borate structures, consisting in a much greater variety of their polyanions, in comparison with silicates, phosphates, etc.…”

“…As distinct from Tennyson' systematic [93], in [91], borates with isolated BO 3 -triangles and BO 4 -tetrahedra are included into the section of insular borates, as well as borates with isolated "mono"-ions and dimmers. The classification described in Ref.…”

“…The classification described in Ref. [91] comprises practically all the borates and many borosilicates known at the time, both with interpreted and hypothetical structures, and reflects the regularities of the polymerization of borates (mainly, hydrated ones). A place was found in it for 119 of the more than six hundreds known by that time anhydrous borates and their polymorphic modifications.…”

“…Finally, it should be noted that in accordance with [23], the first SrB 4 O 7 structure determination by the author of [95] was also incorrect. Namely, based on this example it was assumed possible for the polymerization to take place not only by the combining of the corners of BO 3 -triangles and BO 4 -tetrahedra but also the edges of the tetrahedral [91]. In this connection, it is unlikely that approximately interpreted in [7] layered Na 2 Zn 2 MnB 4.67 O 11 structure with a very close proximity of triple-charged B 3+ can be stable.…”