Borate glasses are useful, but not as common as silicate glasses, in which tetrahedra are linked at corners and arranged in a disordered manner similar to the triangles.

Ordinary window glass is silicate glass, made from sand and metal oxides. Because glasses are made up of disorderly snarls of chains of atoms instead of regular rows in a crystalline lattice, they do not have a definite melting point.

As the temperature is increased, more of the glass structure is loosened, and a glass softens and begins to flow; it continues to flow throughout an appreciable temperature range. We will discuss silicate glasses in more detail in Chapter 6.