The tetrahedral SiO 4 4 ion is known as the orthosilicate ion. It can be regarded as the fundamental
unit in the structures of most complex silicates. Several minerals including phenacite , Be 2 SiO 4 , and
willemite , Zn 2 SiO 4 , contain this ion. Both of these minerals have tetrahedral coordination of SiO 4 4 units
around the metal ion:
O