Q.Describe the basic structural unit found in all silicates. How do orthosilicates, chain silicates and sheet silicates differ in the way this unit is linked together?

[!TLDR] Every silicate is built from the SiO4 tetrahedron; orthosilicates share no corners, chain silicates share 2 corners per tetrahedron, and sheet silicates share 3 corners per tetrahedron. [!ANSWER] All silicates are built from the SiO4^4- tetrahedron; orthosilicates are isolated (unshared) tetrahedra, chain …

Every silicate mineral, however structurally elaborate, is ultimately built from a single repeating unit: the $\text{SiO}_4^{4-}$ tetrahedron, in which a central, $sp^3$-hybridised silicon atom is covalently bonded to four oxygen atoms occupying the corners of a regular tetrahedron. The differences between silicate types arise purely from how many corner oxygens neighbouring tetrahedra share with each other. In an orthosilicate, the tetrahedra share no corners at all — each $\text{SiO}_4^{4-}$ unit stands isolated, its negative charge balanced by surrounding metal cations (e.g. olivine). In a chain silicate (pyroxene-type), each tetrahedron shares exactly two of its four corner oxygens with adjacent tetrahedra, linking them into an infinite, extended one-dimensional chain, with the repeating unit working out to $(\text{SiO}_3)^{2-}$ per silicon. In a sheet silicate, each tetrahedron shares three of its four corners with its neighbours, extending the linkage into a two-dimensional p …

State the common SiO4 tetrahedral building block, then differentiate orthosilicate/chain/sheet silicates purely by the number …

Describing the three silicate types by a vague qualitative difference rather than the precise number of shared corners (0, 2, 3); forgetting that a fully-shared (4-corner) tetrahed …