The hardness and brittleness of ceramic materials are interrelated. Hard materials are more apt to fracture in the vicinity of an indentation during a hardness test, while softer materials tend to plastically deform to the indenter shape without fracturing. Measured hardness, in turn, is affected by both specimen deformation and fracture processes. This interrelationship is examined by means of extensive Vickers hardness testing. A new index of brittleness is proposed.