Crystal structures inherited from parent high-temperature disordered microblocks: Ca2SiO4, Na2SO4–K2SO4 sulfates, and related minerals (bubnovaite and dobrovolskyite)

Abstract

Crystal structures of Ca₂SiO₄, Na₂SO₄–K₂SO₄ sulfates, and related minerals bubnovaite K₂Na₈Ca(SO₄)₆ and dobrovolskyite Na₄Ca(SO₄)₃ were described as consisting of microblocks for the first time. A microblock [M(TO₄)₆] that consisted of an octahedron interlinked by six vertices with six adjacent tetrahedra was considered a structural unit inherited upon cooling from a high-temperature disordered parent unit. The relationship between the parent and inherited microblocks was established. Based on this relationship, 15 possible types of microblocks maintaining a trigonal symmetry were derived. The minerals and compounds structurally related to α-Na₂SO₄-derived superstructures were formed as a result of the cooling of the high-temperature phases containing the disordered parent microblock. Here, the inheritance driving force was the tendency of the structure to become ordered upon cooling. The reasons for the formation of a microblock from the parent microblock were mainly determined by the ionic radius and type of cation occupying the octahedral site. The identification of minerals with the described structural features could be a promising tool for the synthesis of novel compounds with useful properties.