Structure and Topology of Dumortierite and Dumortierite-Like Materials

Abstract

Dumortierite, ca. (Al,)Al 6 (BO 3)Si 3 O 13 (O,OH) 2 , has a complex and unusual crystal structure that is shared by several minerals and an increasing number of synthetic materials, which we group together as dumortierite-like materials (DLMs). Dumortierite has a strongly pseudo-hexagonal orthorhombic structure based on rod-like double-chains of Al octahedra in a framework based on the {6•4•3•4} semi-regular planar tiling. The large hexagonal channels contain chains of face-sharing Al octahedra attached to the framework by rings of SiO 4 tetrahedra. Smaller triangular channels contain planar BO 3 groups, while in other materials the triangular channels are occupied by tetrahedral or pyramidal groups. Holtite and magnesiodumortierite are isostructural with dumortierite, while ellenbergerite, phosphoellenbergerite, ekatite, and the synthetic materials have very similar structures to dumortierite, but with hexagonal symmetry. These minerals and materials differ from one another in the identity of the metal cations occupying the framework and face-sharing chains, and in the tetrahedral, pyramidal, or triangular groups within the hexagonal and triangular channels. We write the following structure-generating function, which describes both topological and stoichiometric properties of DLMs: X(M 2 Φ) 3 (T h Q h 3 q h) 3 (T t Q t 3 q t) where X is the face-sharing hexagonal channel octahedrally coordinated site, M is the framework octahedrally coordinated site, T h and T t are three-to four-coordinate cation sites in the hexagonal and triangular channels, Φ is a four-coordinate anion site, Q h and Q t are three-coordinate basal anion sites, and q h and q t are one-to three-coordinate apical anion sites. We discuss various structural and crystal chemical properties of DLMs, illustrating their commonalities as variations on the theme described by the structure-generating function. We also discuss three closely related structures which involve modifications of different geometrical or topological aspects of the DLM structure: the structure of lyonsite and its synthetic analogues, the structure of satterlyite and holtedahlite, and the structure of the AB polytype of the cancrinite group of feldspathoids.

Mixed-Valence Iron Dumortierite Fe13.52.22+(As5+O4–x)8(OH)6 and Its Intricate Topotactic Exsolution at Mild Temperatures

“…2.22+ (AsO 4−x ) 8 (OH) 6 , an all-iron analogue to the dumortierite structural type, 11 never isolated so far. Its microporous crystal structure involves 1D Fe/O columnar units arranged in a complex hexagonal manner and mainly hold by AsO 4 groups.…”

A novel cobalt sodium phosphate hydroxide with the ellenbergerite topology: crystal structure and physical properties

“…The relationship between the microporous cancrinite-like and rather dense dumortierite-like structure types has been pronounced in the work. 13 Actually, the cell parameters for both hexagonal cobalt phosphate structures, for example, are very similar: a = 12.8514(7) Å, c = 5.0468(5) Å, sp. gr.…”

“…Smaller triangular channels built by CoO 6 polyhedra enclose HPO 4 tetrahedra by means of vertex bridging. This framework with rodlike components 13 is responsible for the needle-like morphology of synthesized crystals (Fig. 1).…”

“…12 All these compounds with porous 3D-frameworks show magnetic interactions between metal centers. In the study, 13 they were called dumortierite-like materials where mineral dumortierite, (Al,Mg,Fe 3+ )Al 6 (O,OH) 3 [BO 3 ][SiO 4 ] 3 , has a similar strongly pseudo-hexagonal but orthorombic structure.…”

Magnetic properties of a new cobalt hydrogen vanadate with a dumortierite-like structure: Co13.5(OH)6(H0.5VO3.5)2(VO4)6

“…The novel cobalt hydrogen vanadate Co 13.5 (OH) 6 (H 0.5-VO 3.5 ) 2 (VO 4 ) 6 is isostructural with Mg 13.4 (OH) 6 (HVO 4 ) 2 -(H 0.2 VO 4 ) 6 (Ðordević et al, 2008) and to the mineral phosphoellenbergerite, Mg 12 (Mg,Fe,&) 2 (PO 4 ,PO 3 OH, AsO 4 ) 6 -(PO 3 OH,CO 3 ) 2 (OH) 6 (Raade et al, 1998). The phosphoellenbergerite mineral and other related structures (Che et al, 2005;Gu et al, 2007;Ni et al, 2009;Amoró s et al, 1996;Mentre et al, 2018) were reported as dumortierite-like materials (Evans & Groat, 2012) due to their similar topology to the mineral dumortierite, i.e. (Al,&)Al 6 (BO 3 )Si 3 O 13 (O,OH) 2 .…”