In a diamond crystal, covalent bonding is present. Diamond is an allotrope of carbon, and each carbon atom in the crystal is bonded to four other carbon atoms in a tetrahedral arrangement. These strong covalent bonds between the carbon atoms create a rigid and stable lattice structure, giving diamond its remarkable hardness and high thermal conductivity. Unlike ionic or metallic bonds, covalent bonds involve the sharing of electrons between atoms, which results in the strong and directional nature of the bonds in diamond.