Icosahedral order in liquids

The possibility of icosahedral order in liquids and its role in glass transition is discussed in a broad context of statistical mechanics of liquid. It is pointed out that the structures of glasses and liquids are described both in terms of the topology of atomic bond networks as well as the local distortion of the atomic bonds. While topology plays a dominant role in covalent glasses, local distortion is likely to be more important for metallic glasses.