Silicate minerals are very common. There are many different structures that include silicate tetrahedra (SiO4)^(4-) building blocks. These blocks can be three dimensionall corner-shared as in quartz cristobalite, isolated as in forsterite, sharing one corner between two tetrahedra as in Akermanite, forming linear chains, or even sheets s in kaolinite and other clays. The incredible diversity of compounds is a result of the flexible bonding and building nature of the tetrahedral unit.