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Why does diamond conduct heat well but electricity poorly?

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A labeled diagram of the periodic table entry for carbon, showing its atomic number 6, symbol C, electron configuration, atomic weight range, solid physical state, hexagonal crystal structure, and weakly acidic oxide properties. Color coding and icons indicate it is a nonmetal, solid at room temperature, with hexagonal structure and weak acidity. — carbon Carbon and its properties.

Diamond’s unique thermal and electrical properties are a direct consequence of its rigid, three-dimensional crystal structure, in which each carbon atom is covalently bonded to four others in a stable tetrahedral configuration.12

Electrical Conductivity

Diamond is an electrical insulator because all of its valence electrons are localized and tightly bound within these strong covalent bonds. Because there are no free or mobile electrons available to carry a charge, diamond cannot conduct electricity.2

Thermal Conductivity

Conversely, diamond is an excellent conductor of heat due to the rigidity of its bonding structure. In condensed-matter physics, heat is transported through solids via phonons—units of vibrational energy arising from oscillating atoms. Because the atoms in diamond are bound into a highly rigid, repeating lattice, these mechanical vibrations travel efficiently throughout the crystal, allowing diamond to conduct heat exceptionally well.34