Boron-rich phases with icosahedral symmetry are quite intriguing. It is important to understand the origin of hardness of boron-rich materials. By starting from a chemical bond viewpoint, a simple method for evaluating hardness of boron-rich phases is presented. This method has been applied to some materials such as alpha-B-12, B13C2, and B12X2 (X = O, P, As), and the predicted hardnesses are in agreement with available experimental values. The results show that this approach provides a powerful tool for predicting superhardness when searching for novel superhard materials in boron-rich phases by first principles.