Carbonado is the toughest form of diamond.

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

Answer: (D)

Toughness is about a material’s ability to resist fracture and absorb energy when struck or stressed, not just how hard it is to scratch. Carbonado stands out because it is a polycrystalline, porous aggregation of many tiny diamond grains fused together. That grain-boundary network helps blunt and deflect cracks, dissipating energy and making the material much tougher than a single crystal of diamond. So, carbonado’s structure gives it exceptional resistance to fracturing, which is why it’s described as the toughest form of diamond.

Graphite, while sharing the same element, has a layered structure that makes it far softer and less resistant to fracture. Nanodiamond refers to tiny diamond particles; their toughness isn’t inherently greater than carbonado’s and can vary. A single-crystal diamond is incredibly hard but, due to its lack of the extensive grain boundaries found in carbonado, its toughness is not as high as that of this polycrystalline form.