Amorphous solids include glass, plastic, gels and thin films. An amorphous solid is one of two types of solid, the other type being crystalline. An amorphous solid has no repeated pattern of orientations and positions of its constituent atoms and the bonds between them.
Amorphous solids are possible in most classes of materials, although crystalline solids are more common. An amorphous solid is often formed by cooling a liquid faster than its constituent atoms can arrange themselves into regular patterns. The properties of many amorphous solids are actually somewhat intermediate between solids and liquids. The differences between crystalline solids in atomic arrangement also leads to differences in the way they behave under different conditions.
Crystalline solids have definite melting or evaporation points, regular geometric shapes and form flat surfaces when broken or cut. Amorphous solids melt over a range of temperatures, rather than just one, and lack the other features of crystalline solids. The distinction between amorphous and crystalline is not an absolute one, however, and many materials actually have properties of both. They are just the extremes of a continuum of solid states. At a microscopic scale, it can be almost impossible to tell the difference between an amorphous solid and a crystalline one.