“Diamonds are the hardest substance known”

For centuries, the extraordinary toughness of diamonds has been widely recognized, leading to their use in everything from jewelry to cutting tools. This remarkable resistance to scratching and abrasion has firmly cemented the idea in public consciousness that diamonds are, without question, the hardest substance known to exist. This long-held understanding is the likely origin of the common misconception.

Scientifically, natural diamond does indeed hold the title for the hardest naturally occurring substance, registering a perfect 10 on the Mohs scale of mineral hardness, which measures scratch resistance. Its unique atomic structure, where carbon atoms form strong covalent bonds in a rigid three-dimensional lattice, is responsible for this exceptional property. However, advancements in materials science have revealed that several synthetic materials can surpass diamond's hardness. For instance, wurtzite boron nitride (w-BN) has been theoretically predicted to have a greater indentation strength than diamond. Another material, lonsdaleite, a hexagonal form of carbon found in meteorites, is also theorized and, in some laboratory syntheses, confirmed to be significantly stiffer and potentially up to 58% harder than conventional cubic diamond under certain conditions.

People commonly believe that diamonds are the absolute hardest substance because the qualifier "naturally occurring" is often omitted in everyday conversation. The widespread industrial application of diamonds for cutting, drilling, and grinding further reinforces this perception of unmatched supremacy. While diamonds are undoubtedly incredibly hard and remain the hardest material found in nature, the cutting edge of material science continues to explore and create new substances with even more extreme properties.