another application of the material sciences is the structures of glass and ceramics, typically associated with the most brittle materials. ceramics and glasses use covalent bonds and ionic-covalent bonds with sio2, silica or sand, as a fundamental building block. ceramics are as soft as clay and as hard as stone and concrete. usually, they are crystalline in form. most glasses contain a metal oxide fused with silica. at high temperatures used to prepare glass, the material is a viscous liquid. glass forms into an amorphous structure when it is cooled. windowpanes and eyeglasses are important examples. fibers of glass are also available. diamond and carbon in its graphite form are considered to be ceramics.