Monoclinic crystal systems are characterized by three axes of unequal length and two axes that are perpendicular to each other. Examples of monoclinic crystals include gypsum and borax.

The unit cell in which the constituent atoms are present only at the corner is known as simple cubic cell. It is also referred to as a primitive cubic cell. In the simple cubic cell, each corner atom is shared by eight different unit cells.

Diamond is an example of a covalent solid, which is a type of solid in which the constituent particles are attached to each other by covalent bonds. Examples of covalent solids include diamond, graphite, silicon, SiC, AIN, and quartz.

There are two polymorphous structures of sulfur, rhombic and monoclinic. Polymorphous structures occur when a single substance can crystallize in two or more forms depending upon the conditions.

Hexaclinic is not a crystal system. The other crystal systems are cubic, tetragonal, rhombohedral or trigonal, orthorhombic or rhombic, monoclinic, triclinic and hexagonal.

The intermolecular forces of attraction in a solid are very strong, making it incompressible. Gases are highly compressible, while liquids are semi-compressible.

Amorphous solids behave like fluids and flow very slowly under the influence of gravity. Therefore, they are considered to be supercooled liquids.

Ice is the only substance that has a lower density as a solid than as a liquid. Its density is 0.92 g/cm3 as a solid and 1 g/cm3 as a liquid. Mercury has a density of 14.184 g/cm3 as a solid and 13.69 g/cm3 as a liquid. Carbon dioxide has a density of 1.56 g/cm3 as a solid and 1.10 g/cm3 as a liquid. NaCl has a density of 2.71 g/cm3 as a solid and 1.556 g/cm3 in molten state.

Crystalline solids are anisotropic, meaning they have different properties in different directions, whereas amorphous solids are isotropic, meaning they have identical properties in all directions. The lack of a clean cleavage, true solidity, and sharp melting points are all characteristics of crystalline solids.

Lattice points are the points at which atoms may be present on the unit cell. They indicate the position of atoms in a crystal.