Tectosilicates-A Three-Dimensional Network

Tectosilicates are characterized by a complete three-dimensional network, in which all four oxygen atoms of the SiO,j-tetrahedra are linked to neighboring tetrahedra. 

Among the tectosilicates the O/Si ratio is 2. When A1 partly replaces Si, the silicate anion becomes more complicated, such as for instance [AlSijOg] . This ion complex is an essential part of feldspar minerals, the most widespread of any mineral group. 

They constitute 60% of the earth s crust Feldspars have no color of their own and are often nearly white. They may however be colored due to impurities. On decomposition, feldspars yield kaoHnite and clay minerals. 

Mineral Formula Crystal form and habit ) Appearance 

Albite (sodium feldspar) NaAlSijOg Triclinic. Plates and rods. A lamellar, leaf-like variety of albite is called cleavelandite A colorless or milky-white mineral 

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