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A group of minerals containing various amounts of the elements Silicon and Oxygen. The Silicates are the largest group of minerals. The construction component of all Silicates is the tetrahedron, which is one Silicon atom equidimensionally placed around four Oxygen atoms.
So, with silicon and oxygen being the two most abundant elements in the crust, the crust is going to be dominated by silicate minerals and oxides (mostly silicates by weight). Depending on weight% silica (SiO2) within these these silicate rocks and minerals, they are classified as being mafic, intermediate, and silicic.