A structure hierarchy for silicate minerals: sheet silicates

Abstract

The structure hierarchy hypothesis states that structures may be ordered hierarchically according to the polymerisation of coordination polyhedra of higher bond-valence. A hierarchical structural classification is developed for sheet-silicate minerals based on the connectedness of the two-dimensional polymerisations of (TO4) tetrahedra, where T = Si4+ plus As5+, Al3+, Fe3+, B3+, Be2+, Zn2+ and Mg2+. Two-dimensional nets and oikodoméic operations are used to generate the silicate (sensu lato) structural units of single-layer, double-layer and higher-layer sheet-silicate minerals, and the interstitial complexes (cation identity, coordination number and ligancy, and the types and amounts of interstitial (H2O) groups) are recorded. Key aspects of the silicate structural unit include: (1) the type of plane net on which the sheet (or parent sheet) is based; (2) the u (up) and d (down) directions of the constituent tetrahedra relative to the plane of the sheet; (3) the planar or folded nature of the sheet; (4) the layer multiplicity of the sheet (single, double or higher); and (5) the details of the oikodoméic operations for multiple-layer sheets. Simple 3-connected plane nets (such as 63, 4.82 and 4.6.12) have the stoichiometry (T2O5)n (Si:O = 1:2.5) and are the basis of most of the common rock-forming sheet-silicate minerals as well as many less-common species. Oikodoméic operations, e.g. insertion of 2- or 4-connected vertices into 3-connected plane nets, formation of double-layer sheet-structures by (topological) reflection or rotation operations, affect the connectedness of the resulting sheets and lead to both positive and negative deviations from Si:O = 1:2.5 stoichiometry. Following description of the structural units in all sheet-silicate minerals, the minerals are arranged into decreasing Si:O ratio from 3.0 to 2.0, an arrangement that reflects their increasing structural connectivity. Considering the silicate component of minerals, the range of composition of the sheet silicates completely overlaps the compositional ranges of framework silicates and most of the chain-ribbon-tube silicates.

A structure hierarchy for silicate minerals: chain, ribbon, and tube silicates

“…In Table 10, all chain-, ribbon-and tube-silicates have been listed from TO 3.0 to TO 2.5 . If the sheet structures of Hawthorne et al (2019) are included, we see a general trend in composition as the degree of polymerisation between (TO 4 ) n− -tetrahedra increases: chains → ribbons → tubes → single sheets → double sheets. This trend is shown in Fig.…”

“…This work provided detailed descriptions of silicate structures to date, and for many years has been the 'go to' source for crystallographers working on comparative aspects of silicate structures. Hawthorne et al (2019) dealt with the large number of silicate minerals by dividing them into four categories and considering them separately according to the dimensional polymerisation of their tetrahedra: (1) cluster silicates that do not show infinite polymerisation; (2) chain, ribbon and tube silicates that are infinitely polymerised in one dimension; (3) sheet silicates that are infinitely polymerised in two dimensions; and (4) framework silicates that are infinitely polymerised in three dimensions. Hawthorne (2015a) and Hawthorne et al (2019) introduced the first comprehensive structure hierarchy for sheet-silicate minerals.…”

“…Hawthorne et al (2019) dealt with the large number of silicate minerals by dividing them into four categories and considering them separately according to the dimensional polymerisation of their tetrahedra: (1) cluster silicates that do not show infinite polymerisation; (2) chain, ribbon and tube silicates that are infinitely polymerised in one dimension; (3) sheet silicates that are infinitely polymerised in two dimensions; and (4) framework silicates that are infinitely polymerised in three dimensions. Hawthorne (2015a) and Hawthorne et al (2019) introduced the first comprehensive structure hierarchy for sheet-silicate minerals. Hawthorne (2015a) represented sheet structures as n-connected plane nets (2 < n ≤ 4), and showed that combining such nets with topological building operations allows one to generate sheet-silicate structures.…”

Fedorite from Murun Alkaline Complex (Russia): Spectroscopy and Crystal Chemical Features

“…According to the silicate minerals hierarchy of [8], fedorite is a sheet silicate with a two-dimensional infinite tetrahedral polymerization. The tetrahedral double layer in fedorite can be considered as a 3-connected net with the designation 6 3 ( Figure S1 of Supplementary Materials).…”

Crystal structures of K-cymrite and kokchetavite from single-crystal X-ray diffraction

“…DOI: https://doi.org/10.2138/am-2020-7407. http://www.minsocam.org/ Since K-cymrite is able to keep its crystalline state after dehydration as well as host different species of fluids in the crystal structure (Sokol et al 2019), materials with similar structure (Hawthorne et al 2019) can be prospective sorbents and/or catalysts: BaAl 2 Si 2 O , hexacelsian (Galuskina et al 2017) This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change.…”