Glass is an inorganic product of fusion that has cooled to a rigid state without crystallizing. According to the Center for Glass Research at the New York State College of Ceramics at Alfred University:[1]
There are four basic states of matter: solid, liquid, gas, and plasma. In a solid, molecules are ordered in a structured way, called a lattice. In a liquid, molecules are disordered and they are not rigidly bound. In a glass, however, we have the unique characteristic of a solid whose molecules are not ordered yet they are still rigidly bound. This situation has caused some chemists to refer to glass as a "supercooled liquid" rather than a solid. This would be a different state of matter than, say, freezing water; as water passes below the freezing point and becomes ice it forms a crystal and exhibits the properties of a standard crystalline solid.[2]
Glass is produced industrially by melting a mixture of calcium carbonate (limestone), sodium carbonate (soda), and silicon dioxide, which is a major component of sand. Quartz sand, which is rich in silicon dioxide, is the most commonly used type of sand. The subsequent product, once cooled, is glass.