Covalent network solids there are no individual molecules, the atoms in the crystal lattice are all directly linked by covalent bonds, so that in the crystal no single molecules can be identified (the crystal can be seen as a single macromolecule); are included crystals of diamond, silicon, some other nonmetals, and some covalent compounds such as silicon dioxide (sand) and silicon carbide (carborundum, the abrasive on sandpaper). Many minerals have networks of covalent bonds to all the surrounding atoms in a continuous network, resulting in huge crystals.
To break or to melt a covalent network solid, covalent bonds must be broken. Because covalent bonds are relatively strong, covalent network solids are typically characterized by hardness, strength, and high melting points. They do not dissolve in water, nor do they conduct electricity.