tektosilicates

Tektosilicates, or framework silicates, constitute a major class of silicate minerals in which all four oxygen atoms of each SiO4 tetrahedron are shared with neighboring tetrahedra. This sharing produces a three-dimensional, rigid framework in which silicon (and often aluminum) occupies tetrahedral coordination with oxygen. When aluminum substitutes for silicon in the framework, the structure carries negative charges that are balanced by extra‑framework cations such as sodium, potassium, or calcium, and sometimes by water in larger cavities found in specific members.

The most familiar tektosilicates are quartz and the feldspars. Quartz is a pure silicate with the framework composed entirely of SiO4 tetrahedra and its formula is SiO2. Feldspars include alkali feldspars (such as orthoclase, microcline, and sanidine, with the formula KAlSi3O8 or related compositions) and the plagioclase series (ranging from NaAlSi3O8 to CaAl2Si2O8). In these minerals, aluminum substitutes for some silicon in the framework, and the resulting charge is balanced by interstitial alkali or alkaline earth cations.

Zeolites are another important subgroup of tektosilicates, featuring aluminosilicate frameworks with channels and cages that host water molecules and exchangeable cations. This porosity gives zeolites distinct physical properties and useful industrial applications.

Tektosilicates are among the most abundant minerals in Earth's crust, forming a large portion of continental rocks. They are distinguished from other silicate groups by their fully polymerized, three-dimensional frameworks, which impart characteristic hardness, cleavage, and structural stability.