Answer
The silicate tetrahedrons can also form structures called pyrosilicates (or sorosilicates) in which two tetrahedrons share one corner, forming the disilicate ion, which has the formula $Si_{2}O_{7}^{6-}$.
Work Step by Step
The silicate tetrahedrons can also form structures called pyrosilicates (or sorosilicates) in which two tetrahedrons share one corner, forming the disilicate ion, which has the formula $Si_{2}O_{7}^{6-}$. This group requires cations that balance the 6 - charge on $Si_{2}O_{7}^{6-}$ . Again, these cations can be the same metal ions or a mixture of different metal ions. For example, in the mineral hardystonite ($Ca_{2}ZnSi_{2}O_{7}$), two $Ca^{2+}$ ions and one $Zn^{2+}$ ion together provide the 6 + charge.
