Glass acts like a liquid but stays frozen like a solid

Unlike ice, which forms a neat, repeating crystal lattice when water freezes, glass is a structural mess. As molten silica cools, its molecules move slower and slower until they simply lock in place, trapped in the chaotic arrangement of a liquid but with the unyielding strength of a solid. This state is so strange that physicists still debate whether glass is a true solid or just a 'supercooled liquid' that is moving too slowly for us to notice.