Types of silicate structure ?

Independent (isolated) tetrahedra with no shared oxygens (cations added), Si:O ratio = 1:4, olivine. 2) Ring silicates (less important geologically): cyclic rings of 6 tetrahedra, share 2 oxygens, Si:O ratio = 1:3, tourmaline, beryl. 3) Chain silicates: long chains of linked tetrahedra; two subgroups (a) single chains share 2 oxygens, Si:O ratio = 1:3, pyroxene. (b) double chains share 2.5 oxygens, Si:O ratio = 4:11, amphibole. 4) Sheet silicates: continuous flat sheet (extension of double chain structure in 2 dimensions), share 3 oxygens, Si:O ratio = 2:5, kaolinite and other clay minerals. 5) Framework silicates: 3-dimensional network of shared tetrahedra, share all 4 oxygens, Si:O ratio = 1:2, quartz and feldspar. Quartz = SiO2, electrically neutral, no extra cations added