trioctahedral structure

chemistry

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July 14, 2026

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In chemistry, "trioctahedral" describes a structure where all three available octahedrally coordinated positions are occupied. This term is particularly relevant in the context of clay minerals, specifically the serpentine group. In these minerals, the general structural formula involves cations in an octahedral sheet. For trioctahedral species, these cations are typically magnesium, iron, manganese, or nickel. Examples of trioctahedral clay minerals include chrysotile, antigorite, and lizardite, all with the formula Mg₃Si₂O₅(OH)₄. The arrangement and fit between the tetrahedral and octahedral sheets influence the morphology of these minerals.12

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clay mineral
General features
…of octahedral sheet is called trioctahedral, and the latter dioctahedral. If all the anion groups are hydroxyl ions in the compositions of octahedral sheets, the resulting sheets may be expressed by M²⁺(OH)₂ and M³⁺(OH)₃, respectively. Such sheets, called hydroxide sheets, occur singly, alternating with silicate layers in some clay minerals.…
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…of octahedral sheet is called trioctahedral, and the latter dioctahedral. If all the anion groups are hydroxyl ions in the compositions of octahedral sheets, the resulting sheets may be expressed by M²⁺(OH)₂ and M³⁺(OH)₃, respectively. Such sheets, called hydroxide sheets, occur singly, alternating with silicate layers in some clay minerals.…
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