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The paper discusses the material removal process in refractory ceramics eroded by hydro-abrasive jets. In particular, bauxite, sintered magnesia, and magnesia chromite are eroded. The influence of abrasive particle velocity, local exposure time, abrasive mass-flow rate, and abrasive type is investigated. Erosion depth, specific erosion rate, and geometry of the generated cavities are measured and analysed. For particle velocity as well as for local exposure time, threshold conditions are identified. At low erosion intensity, target material properties and abrasive type do not affect the material removal process notably. From optical and SEM-microscopy it is further found that the material removal mode changes with the progression of the erosion process. In the upper region of the eroded kerf, the dominating material removal mode is the simultaneous cutting of matrix and inclusion grains (transgranular). In the lower range, the erosion process is characterised by the removal of the binding matrix followed by washing off the inclusion grains (intergranular). The balance between both modes depends on the energy delivered to the erosion site. These observations are explained by assuming a continuous loss in kinetic energy of the abrasive particles during HAE. Some features of non-linear fracture are noticed and suggestions are made how to use non-linear fracture parameters to evaluate erosion resistance.