Materials Data on RbMg6SiO8 by Materials Project
RbMg6SiO8 is Caswellsilverite-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Rb is bonded to six O atoms to form RbO6 octahedra that share corners with two equivalent SiO6 octahedra, corners with four equivalent RbO6 octahedra, and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.35 Å) and two longer (2.49 Å) Rb–O bond lengths. There are three inequivalent Mg sites. In the first Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, edges with four equivalent SiO6 octahedra, and edges with eight equivalent MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.07 Å) and four longer (2.35 Å) Mg–O bond lengths. In the second Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, edges with four equivalent RbO6 octahedra, and edges with eight equivalent MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.11 Å) and four longer (2.35 Å) Mg–O bond lengths. In the third Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six equivalent MgO6 octahedra, edges with two equivalent RbO6 octahedra, edges with two equivalent SiO6 octahedra, and edges with eight MgO6 octahedra. The corner-sharing octahedra tilt angles range from 0–20°. There are a spread of Mg–O bond distances ranging from 2.08–2.38 Å. Si is bonded to six O atoms to form distorted SiO6 octahedra that share corners with two equivalent RbO6 octahedra, corners with four equivalent SiO6 octahedra, and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (1.69 Å) and four longer (2.35 Å) Si–O bond lengths. There are five inequivalent O sites. In the first O site, O is bonded to one Rb, four equivalent Mg, and one Si atom to form distorted ORbMg4Si octahedra that share corners with six equivalent ORbMg4Si octahedra and edges with twelve OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–20°. In the second O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with six equivalent OMg6 octahedra and edges with twelve ORbMg4Si octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the third O site, O is bonded to four Mg and two equivalent Si atoms to form OMg4Si2 octahedra that share corners with six OMg4Si2 octahedra and edges with twelve ORbMg4Si octahedra. The corner-sharing octahedral tilt angles are 0°. In the fourth O site, O is bonded to two equivalent Rb and four Mg atoms to form ORb2Mg4 octahedra that share corners with six OMg4Si2 octahedra and edges with twelve ORbMg4Si octahedra. The corner-sharing octahedral tilt angles are 0°. In the fifth O site, O is bonded to two equivalent Rb and four Mg atoms to form ORb2Mg4 octahedra that share corners with six OMg4Si2 octahedra and edges with twelve ORbMg4Si octahedra. The corner-sharing octahedral tilt angles are 0°. Both O–Mg bond lengths are 2.08 Å.