silicon is replaced by an atom of lower valence such as aluminum. Al for Si substitution is common. Nesosilicates or orthosilicates Nesosilicates (from Greek 'island'), or orthosilicates, have the orthosilicate ion, which constitute isolated (insular) tetrahedra that are connected only by interstitial cations. The Nickel–Strunz classification is 09.A –examples include: Phenakite group Phenakite – Willemite – Olivine group Forsterite – Fayalite – Tephroite – Garnet group Pyrope – Almandine – Spessartine – Grossular – Andradite – Uvarovite – Hydrogrossular – Zircon group Zircon – Thorite – Hafnon – group Andalusite – Kyanite – Sillimanite – Dumortierite – Topaz – Staurolite – Humite group – Norbergite – Chondrodite – Humite – Clinohumite – Datolite – Titanite – Chloritoid – Mullite (aka Porcelainite) – Sorosilicates Sorosilicates (from Greek 'heap, mound') have isolated pyrosilicate anions , consisting of double tetrahedra with a shared oxygen vertex—a silicon:oxygen ratio of 2:7. The Nickel–Strunz classification is 09.B. Examples include: Thortveitite – Hemimorphite (calamine) – Lawsonite – Axinite – Ilvaite – Epidote group (has both and groups} Epidote – Zoisite – Tanzanite – Clinozoisite – Allanite – Dollaseite-(Ce) – Vesuvianite (idocrase) – Cyclosilicates Cyclosilicates (from Greek 'circle'), or ring silicates, have three or more tetrahedra linked in a ring. The general formula is (SixO3x)2x−, where one or more silicon atoms can be replaced by other 4-coordinated atom(s). The silicon:oxygen ratio is 1:3. Double rings have the formula (Si2xO5x)2x− or a 2:5 ratio. The Nickel–Strunz classification is 09.C. Possible ring sizes include: Some example minerals are: 3-member single ring Benitoite – 4-member single ring Papagoite – . 6-member single ring Beryl – Bazzite – Sugilite – Tourmaline – Pezzottaite – Osumilite – Cordierite – Sekaninaite – 9-member single ring Eudialyte – 6-member double ring Milarite – Note that the ring in axinite contains two B and four Si tetrahedra and is highly distorted compared to the other 6-member ring cyclosilicates. Inosilicates Inosilicates (from Greek [genitive: ] 'fibre'), or chain silicates, have interlocking chains of silicate tetrahedra with either , 1:3 ratio, for single chains or , 4:11 ratio, for double chains. The Nickel–Strunz classification is 09.D – examples include: Single chain inosilicates Pyroxene group Enstatite – orthoferrosilite series Enstatite – Ferrosilite – Pigeonite – Diopside – hedenbergite series Diopside – Hedenbergite – Augite – Sodium pyroxene series Jadeite – Aegirine (or acmite) – Spodumene – Pyroxferroite - Pyroxenoid group Wollastonite – Rhodonite – Pectolite – Double chain inosilicates