Diamonds Practice Test 2026 – Complete Exam Prep

Toughness in diamonds is influenced by crystal structure, especially how cracks move through the material. An aggregate of small crystals, with many grain boundaries, can deflect and arrest cracks more effectively than a single crystal, dissipating more energy as a fracture tries to propagate. Carbonado fits this idea perfectly: it is a polycrystalline, porous aggregate of tiny diamond grains bound together. That network of interfaces makes it highly resistant to fracture, giving it exceptional toughness compared with other diamond forms. In contrast, crustal and mantle diamonds are typically large single crystals formed in those environments, and blue diamonds are color varieties of standard single-crystal diamonds; neither is defined by an aggregate microstructure that boosts toughness. So carbonado is the form described as an aggregate of small crystals and among the toughest.