The type of bonding present in a diamond crystal is covalent bonding. In a diamond, each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement. This strong covalent bonding results in a rigid, three-dimensional lattice structure, which gives diamond its exceptional hardness and high thermal conductivity. The covalent bonds in diamond are responsible for its unique properties, such as its transparency, high refractive index, and ability to cut through other materials.