Q.What makes a glass different from a solid such as quartz? Under what conditions could quartz be converted into glass?

In quartz the $SiO_4$ tetrahedra are linked in a regular, ordered 3-D network (crystalline, long-range order). In glass the same tetrahedra are joined irregularly, giving only short-range order (amorphous). Quartz can be turned into glass by melting it and then cooling it rapidly so the particles cannot re-order.

What distinguishes glass from quartz.

Both are made of $SiO_4$ tetrahedra, but:

• Quartz is a crystalline solid — the tetrahedra are arranged in a regular, repeating pattern with long-range order; it is anisotropic and has a sharp melting point.
• Glass is an amorphous solid — the tetrahedra are linked in an irregular way, giving only short-range order; it is isotropic and softens over a range of temperature (a super-cooled liquid).

Converting quartz to glass.

Quartz is first melted and then the melt is cooled very quickly. Rapid cooling does not give the $SiO_4$ tetrahedra enough time to arrange themselves in the ordered crystalline pattern, so a disordered (amorphous) glass results.

Contrast on the ordered-vs-disordered basis (both are $SiO_2$), then note that rapid cooling of molten quartz freezes in the disorder to give glass.

• Claiming glass and quartz have different chemical composition (both are $SiO_2$).
• Saying slow cooling gives glass — slow cooling would recrystallise it.
• Omitting the "melt first" step.