Question

Why do solids have a definite volume and under what conditions one may convert quartz to glass?

Answer 1

There are in total five states of matter, which are as follows, Solids, Liquids, Gaseous, Bosons and Plasma. Out of all the states of matter the highest attractive molecular forces are in solids. Apart from having highest attractive forces among the particles, the particles do oscillate but to their mean position only. Thus solids are very rigid.

Complete answer:
Solid is that state of matter, which has a definite shape, volume and is rigid. The constituents of the solids are so small and tightly packed that they do not show very frequent vibrations or oscillate too far from the mean positions. That means that for a state to be solid the constituents should not move or vibrate or oscillate too much from its position. This leads to having a fixed volume to solids with a definite shape and lots of rigidness.
The solids can be classified on the bases of the fashion of arrangement i.e., iff regular fashion is observed, then they are said to be crystalline solids, but if the irregular fashion is observed, then they are said to be amorphous solids.
Quartz are hard, crystalline solids that means they have a regular arrangement of atoms or molecules. Glass is an amorphous solid that means they do not have regular arrangements of atoms in them. A crystalline solid can be converted to amorphous solid when excess heat is supplied to them. Thus a quartz can get converted to crystalline solid when heated. The temperature required for necessary conversion is ${2000^\circ }C$ .

Note:
Apart from amorphous solids, iff the arrangement of atoms are not regular, then they are also termed as supercooled liquids or pseudo solids. Supercooled because, on cooling of the liquids the liquids get converted to the solids like water at ${0^\circ }C$ gets converted to supercooled solid commonly called the ice.