sentence: Ceramics are as soft as clay and as hard as stone and concrete.
sentences_before: 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.
sentences_after: 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.
concept_name: ceramic
headings: Materials science Ceramics and glasses