Quartz, $Si{O}_2$ is the most common mineral found on the surface of earth. What is the best explanation for the fact that quartz is hard and has a high melting point ?

Quartz crystals are extended structures in which each atom forms strong covalent bonds with all of its neighbouring atoms

Silicon and oxygen atoms are especially form strong bonds

Quartz crystals are formed under extremes of temperature and pressure

Quartz crystals consist of positive and negative ions that are attracted to one another