Extreme mechanical hardness (ca. 90 GPa) and wear resistance Highest bulk modulus (1.2 × 1012 N m−2) Lowest compressibility (8.3 × 10−13 m2 N−1) Highest room temperature thermal conductivity (2 × 103 W m−1 K−1) Thermal expansion coefficient at room temperature very low (1 × 10−6 K) Broad optical transparency from the deep ultraviolet to the far infrared Highest sound propagation velocity (17.5 km s−1) Very good electrical insulator (room temperature resistivity is ca. 1013 Ω cm) Diamond can be doped, becoming a semiconductor with a wide bad gap of 5.4 eV Very resistant to chemical corrosion Biologically compatible Low or ‘negative’ electron affinity surface