What is the toughest form of diamond?

• A. Graphite
• B. Nanodiamond
• C. Carbonado
• D. Diamond

Answer: (C)

Toughness is about how well a material resists fracturing and crack propagation under impact or stress, not how hard it is to scratch. Diamond’s single-crystal form is incredibly hard but can be relatively brittle, meaning it can cleave or crack. Carbonado, a natural polycrystalline aggregate of diamond grains bonded together with a porous network, absorbs and deflects cracks, distributing stress and resisting fracture more effectively than a single crystal. Graphite is much softer and slips easily between layers, so it isn’t tough. Nanodiamond refers to tiny diamond particles, which don’t form a bulk material known for exceptional toughness, unlike carbonado. Therefore, the toughest form of diamond is carbonado.