We present the data of a mode-I fracture experiment. The samples are broken under imposed
pressure. The acoustic emission of microfractures before the breakup of the sample is registered. From
the acoustic signals, the position of microfractures and the energy released are calculated. A measure
of the clustering of microfractures yields information about the critical load. The statistics from energy
measurements strongly suggest that the fracture can be viewed as a critical phenomenon; energy events
are distributed in magnitude as a power law, and a critical exponent is found for the energy near fracture.