In condensed matter physics, an amorphous or non-crystalline solid is a solid that lacks the long-range order characteristic of a crystal.Term has been used synonymously with glass. Nowadays,"amorphous solid" is considered to be the overarching concept, and "glass" the more special case: A glass is an amorphous solid that transforms into a liquid upon heating through the glass transition. Other types of amorphous solids include gels, thin films, and nanostructured material. Crystalline solid (or crystal) is a solid material whose constituent atoms, molecules, or ions are arranged in an ordered pattern extending in all three spatial dimensions. In addition to their microscopic structure, large crystals are usually identifiable by their macroscopic geometrical shape, consisting of flat faces with specific, characteristic orientations.