Knowra Tectosilicate framework Tectosilicate framework A silicate structure where every tetrahedron shares all four corners with neighbors, forming a fully connected three-dimensional framework with cavities.
Silicon–oxygen tetrahedron : A silicon atom bonded to four oxygens at tetrahedral corners; the basic building unit of all silicate structures. Every tetrahedron in a tectosilicate shares all four of its oxygen corners with neighboring tetrahedra.
Silicate mineral classification : The grouping of silicate minerals by how their tetrahedra link: isolated, chains, sheets, or frameworks. Tectosilicates are the fully polymerized end of this classification, sharing all tetrahedral corners.
Albite : The sodium end-member of plagioclase feldspar, NaAlSi3O8, a triclinic tectosilicate forming white to colorless crystals. Its structure is a fully connected framework whose cavities hold exactly one sodium per aluminum tetrahedron.
Molecular sieves : Framework materials whose uniform pore sizes separate molecules by dimensions rather than chemistry. A direct technological exploitation of the tectosilicate cavity structure.
Zeolite synthesis : Growing zeolite frameworks under hydrothermal conditions, often with organic templates directing pore structure. Why particular framework topologies nucleate is still not fully predictable.
Aluminum substitution for silicon : Replacement of Si4+ by Al3+ in a tetrahedron, leaving the framework one negative charge per substitution. Substitution is why frameworks like albite's need extra cations such as sodium to balance charge.
Silica polymorphs : Quartz, tridymite, cristobalite, and coesite: pure SiO2 frameworks without any charge-balancing cations. These are tectosilicates with no aluminum substitution, the pure-silica limiting case.
Quartz : The most common silica polymorph, SiO2, a dense three-dimensional framework with no extra cations. The pure-silica framework case, needing no charge balance at all.
Ion exchange : The reversible swapping of extra-framework cations in a framework without restructuring it. Possible only because charge-balancing cations sit loosely in cavities, not bonded into the framework.
Template-directed crystallization : Use of organic molecules as structural molds around which framework tetrahedra assemble during synthesis. The main tool for making frameworks, yet its mechanism remains partly empirical.
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