When quartz is a crystalline solid, why is quartz glass amorphous?


Quartz glass, also known as fused silica, is glass made […]

Quartz glass, also known as fused silica, is glass made by melting and quenching of quartz. Glass has no regular, repeatable molecular structure. In contrast, the silicon and oxygen atoms in quartz form a tetrahedron with a very special arrangement. For details, see the quartz structure.

The rapid quenching of the silica melt prevents the nucleation of crystal "seeds" and prevents the crystal form from propagating throughout the growing solid. In contrast, the disordered state that exists in the melt / liquid remains in the solid.

Fused silica is very tough and has a very low coefficient of thermal expansion. If you bake a small fused silica core on a Bunsen burner and then put it in liquid helium, but the fused silica cylinder has not experienced phase / damage / breakage at all. On the contrary, the same treatment, the difference is that the use of liquid nitrogen to form a similar core quartz will cause the quartz to produce a high degree of fracture.

Quartz does not necessarily grow from aqueous solutions. It can grow well from magma, for example, quartz in granite does not grow from aqueous liquids.