sheets, silicates, clays and micas

what is the structure of a sheet silicate?

each tetrahedron shares 3 out of 4 of its oygens to give an infintite 2 dimensional tetrahedral sheet

what is the repeat unit of sheet silicates?

(Si₂O₅,)^2-

what is added to make a sheet silicate a tetrahedral sheet?

contains spaces in the oxygens which can accomadate hydroxyl ions

what is the repeating unit of a tetrahedral sheet?

[(SiO₂O₅)(OH)]^3-

what is an octahedral sheet?

sites to hold magnesium and aluminum ions may be created by adding a layer of hydroxyl ions onto the tetrahedral sheet

what is the chemical formula for an octahedral sheet?

(si₂O₅)(OH)₄^6-

what is the difference between kaolinite and serpentine?

Kaolinite has 2 out of 3 of the octahedral sites occupied and is a dioctahedral sheet silicate. Serpentine has 3 out of 3 octahedreal sites occupied and is a trioctahedral sheet silicate

what is the chemical formula of kaolinite?

Al₂(Si₂O₅)(OH)₄

what is the chemical formula of serpentine?

(Mg,Fe)₃(Si₂O₅)(OH)₄

what is the structure of talc?

two octahedral sheets linking together face to face

why has talc got a low hardness of 1?

each octahedral layer is electrostatically neutral and thus the forces between sandwiches will be extremely weak

what is the chemical formula of talc?

[(si₄O₁₀)(OH)₂]^6-

what is the diffrence between mica and talc?

one of the si⁴⁺ in the tetrahedral sheet is replaced by Al³⁺ then the compoistion of the sandwiches. this has created an extra negative charge on the sandwich which is balanced by K⁺ which is situated between the layers