A diamond can slice through an ice cube like a hot knife through butter because it is an incredible heat conductor.

Diamonds are the most effective natural thermal conductors on Earth. At room temperature, a high-quality diamond has a thermal conductivity of approximately 2,200 Watts per meter-Kelvin. This is roughly five times higher than copper, which is the standard material for heat sinks and electrical wiring. This extreme efficiency is due to the strong covalent bonding of carbon atoms in a rigid crystal lattice structure.In most materials, heat is transferred by the movement of electrons, but in diamonds, heat moves through lattice vibrations called phonons. These phonons travel through the stiff diamond structure with very little resistance. This allows heat to move at incredible speeds, which is why a diamond feels cold to the touch. It is literally pulling the heat away from your skin faster than other materials.This property was famously documented by the Gemological Institute of America (GIA) and remains a primary method for gemstone identification. Since the 1970s, handheld thermal conductivity testers have been standard tools for jewelers. While materials like cubic zirconia are excellent thermal insulators, real diamonds transfer heat so quickly that they can melt ice almost instantly without being pre-heated.Interestingly, synthetic diamonds grown in labs can sometimes exceed the thermal conductivity of natural stones. Researchers at institutions like the Naval Research Laboratory have studied these properties for use in high-power electronics. By using diamonds as a substrate, engineers can prevent microchips from overheating, extending the life of advanced technology.