SPECIAL SPATIAL SYMMETRY OF MINERAL STRUCTURES

Abstract

Formation of mineral structures is affected both by energetic and crystal chemical barriers: limitations of possible choice of positions of structural units in a crystal lattice caused by features of its Fedorov group. The correspondence of structures of thermodynamically instable mineral phases to priority (most likely) crystal chemical types provides for their kinetic stability. At the same time, crystallization of rare structure is possible only upon conditions of its energetic stability, because the rarity of the Fedorov group indicates its low «crystal chemical feasibility» of the corresponding structure. The phenomenon of rare Fedorov groups is stable, since it is caused by fundamental crystal chemical reasons. It is most striking in a framework structure of a crystal lattice, because the mineral phases can contain 24 various types of 3D-periodical framework structures. The minerals with framework structure can exhibit the effect of supersymmetry, i.e., stability of the structure with chemically identical but symmetrically independent structural units. This effect may be typical of framework structures corresponding to Fedorov groups P42m, P4m2, I 42m, I 4m2, P222, C222, F222, I222, P23, F23, I23, P432, P42 32, F432, P422, I422, P42 22, P62 22 and P64 22. In particular, this structural effect is typical of cubic modification of lazurite with Fedorov group P23.

Keywords

• mineral structure
• spatial symmetry
• fedorov group
• framework structure
• supersymmetry