The crystal structure of ginorite, Ca2[B14O20(OH)6]·5H2O, and the analysis of dimensional reduction and structural complexity in the CaO–B2O3–H2O system

The crystal structure of ginorite, Ca 2 [B 14 O 20 (OH) 6 ]·5H 2 O, from the Chelkar salt dome, western Kazakhstan, has been refined at 150(2) and 296(2) K. The mineral is monoclinic, P 2 1 / c , unit-cell parameters are (at 150/296 K): a = 12.738(1)/12.728(1), b = 14.240(1)/14.303(1), c = 12.750(1)/12.755(1) A, β = 101.163(2)/101.147(2)°, V = 2268.9(4)/2278.3(4) A 3 , Z = 4. The crystal structure is isotypic to that of strontioginorite and is based upon 2-dimensional anionic layers with the composition [B 14 O 20 (OH) 6 ] 4− . The layers are coplanar to (0 1 0) and are composed of BO 4 tetrahedra and BO 3 triangles. The fundamental building block (FBB) for the crystal structures of ginorite and strontioginorite consists of eight BO 3 triangles and six BO 4 tetrahedra. The adjacent FBBs are linked by sharing O atoms to form layers that possess open nine-membered rings centered by the M 1 and M 2 metal atoms. In the crystal structure of strontioginorite, the M 1 and M 2 sites are occupied by Sr and Ca, respectively, whereas, in ginorite, both sites are occupied by Ca. The Ca ↔ Sr substitution affects the geometry of the M 1O 8 polyhedron significantly, with the difference |Δ| between the Sr–O and Ca–O bond lengths up to 0.157 A. The dimensional reduction, structural and chemical complexity of 45 minerals and inorganic compounds of the CaO–B 2 O 3 –H 2 O system have been analyzed using ternary diagrams. The structures with 0-dimensional structural units (finite clusters) constitute 53.3% (24) of all structures in the system, whereas 1-, 2- and 3-dimensional borate polyanions have been observed in 15.6% (7), 20.0% (9) and 11.1% (5) of all structures in the system, respectively. The average structural complexity for the 42 B-bearing phases in the CaO–B 2 O 3 –H 2 O system is 353 bits/cell agrees well with the average complexity of 340 bits/cell for all boron minerals. Ginorite belongs to the class of very complex structures (1536.000 bits/cell) and is the second in complexity in the system after alfredstelznerite, Ca 4 (H 2 O) 4 [B 4 O 4 (OH) 6 ] 4 ·15H 2 O (4026.707 bits/cell). In general, structural and chemical complexities correlate with each other and indicate the presence of the high-complexity areas in the H 2 O dominant part of the diagram, in a band between ca . 10 and 20 mol% CaO.