Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). It is characterized by structural rigidity and resistance to changes of shape or volume. The atoms in a solid are tightly bound to each other, either in a regular geometric lattice (crystalline, such as metals and ordinary ice) or irregularly (amorphous, such as window glass). The atoms, molecules, or ions which make up solids may be arranged in an orderly repeating pattern, or they could be arranged irregularly. Materials whose constituents are arranged in a regular pattern are known as crystals. In some cases, the regular ordering can continue unbroken over a large scale, for example diamonds, where each diamond is a single crystal.
