Why is a glass window a mixture?

A glass window is considered a mixture because it is composed of various materials, primarily silica (sand), along with soda ash and lime, which are mixed together to form glass. These components do not chemically bond in a fixed ratio, allowing for variations in properties such as color and clarity. Additionally, impurities or additives can be included, further emphasizing its heterogeneous nature. Thus, glass can be seen as a mixture rather than a pure substance.