Crack initiation and propagation have been investigated under tensile and shear loading in ceramically and carbon bonded refractories. A wedge splitting test procedure and a modified shear test have been applied. Test results have been used for material characterization especially with respect to brittleness. Furthermore a microscopic fractographic test procedure was developed and applied on fractured test specimens. In order to explain brittleness dependence on structure properties correlation of fractographic and fracture mechanical results has been evaluated. Frequently brittleness reduction is achieved by a lower amount of transgranular crack propagation associated with a strength decrease while maintaining specific fracture energy unchanged. Deviations from pure linear fracture mechanics increase with decreasing brittleness and contribute to specific fracture energy. Shear specimens may show two generations of cracks, a first one initiated by tensile loads (stable propagation) and a second one by shear loads (unstable propagation)