Tectosilicate

see also: Etymology of Tectosilicate

The tectosilicates define a type of architecture of the Silicate S, that with maximum polymeration; structure with space frame; the Si/O report/ratio is equal to 0,5.

The tectosilicates are mineral formed by association of tetrahedral elementary reasons (^4-) by all their tops. In fact the tetrahedrons (polyhedral which have 4 faces, 6 sides and 4 tops) basic ^4- which one finds in all the Silicate S, are welded here by their four tops and each oxygen is related to two cations.

The tectosilicates include/understand several mineral among most important of the Earth's crust. If one leaves the tetrahedron ^4- and that one shares each oxygen between two tetrahedrons, one obtains the formula of the Silice, SiO₂, which in nature is presented into different polymorphic (quartz, Tridymite, Cristobalite etc) and is the constituent main thing of the Verre. One can derive the chemical formula from the others tectosilicates from that of the Silice, generalized in N TO₂, where T indicates the tetrahedral cation, primarily Silicium or Aluminum. The negative charge, which results from the replacement of the Silicium by the Aluminum in the tetrahedrons, is compensated by the presence of the cations M (K, Na, Ca, Ba, Li…) in the cavities of the structure. This characteristic is common to the Feldspath S, the Feldspathoïde S and the Zéolithe S, but topology is different in the three cases.

* N = 1, SiO₂: Quartz, Tridymite, Cristobalite, Kéatite, Coésite, Stishovite

* N = 2, MT₂O₄, Feldspathoïde S with structure quartz or Tridymite: β- Eucriptite (LiAlSiO4), Kalsilite KAlSiO₄ Nephelite Na₃KAl₄Si₄O₁₆ Carnégieite NaAlSiO₄

* N = 3, MT₃O₆, Feldspathoïde S with structure Cristobalite: Leucite KAlSi₂O₆ Pollucite CsAlSi₂O₆·H₂O Analcime NaAlSi₂O₆·H₂O

* N = 4, MT₄O₈, Feldspar S: Orthoclase KAlSi₃O₈, White feldspar NaAlSi₃O₈, Anorthite CaAl₂Si₂O₈, Celsian BaAl₂Si₂O₈

* N > 4, Zeolite S

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