Glass is an amorphous inorganic non-metallic material, generally made of a variety of inorganic minerals (such as quartz sand, borax, boric acid, barite, barium carbonate, limestone, feldspar, soda ash, etc.) as the main raw material, in addition to a small amount of auxiliary raw materials. Its main components are silicon dioxide and other oxides. The chemical composition of ordinary glass is Na2SiO3, CaSiO3, SiO2 or Na2O-CaO-6SiO2, etc. The main component is a silicate compound salt, which is an amorphous solid with no regular structure. It is widely used in buildings to insulate and transmit light, and is a mixture. There is also tinted glass, which is mixed with certain metal oxides or salts to reveal its colour, and tempered glass, which is made by physical or chemical means. Some transparent plastics (e.g. polymethyl methacrylate) are also sometimes referred to as Plexiglas.