Bone mineral and bone organic are assumed to be a linearly elastic, brittle material. A simple micromechanical model based on the shear lag theory is developed to model the stress transfer between the mineral platelets of bone. The bone mineral platelets carry most of the applied load while the organic primarily serves to transfer load between the overlapped mineral platelets by shear. Experiments were done to elucidate the mechanism of failure in bovine cortical bone and to decrease the mineral content of control bone with in-vitro fluoride ion treatm ents. It was suggested that the failure at the ultrastructural level is due to the transverse failure of bonds between the collagen microfibrils in the organic matrix. However, the shear stress transfer and the axial load bearing capacity of the organic is not impaired. Hence, it is assumed that the shear strain in the matrix increases while the shear stress remains constant at the shear yield stress once the matrix starts yielding at the ends of the bone mineral. When the shear stress over the length of the mineral platelet reaches the shear yield stress, no more applied stress is carried by the bone mineral platelets while the organic matrix carries the increased axial load. The bone fails when the axial stress in the organic reaches its ultim ate stress. The bone mineral is assumed to dissolve due to in-vitro fluoride ion treatments and precipitate calcium fluoride or fluoroapatite like material. The amount of dissolution is estimated based on ¹⁹F Nuclear Magnetic Resonance or a decrease in the carbonate content of bone. The dissolution of bone mineral is assumed to increase the porosity in die organic. We assume that the elastic modulus and the ultim ate strength of the organic decrease due to the increased porosity. A simple empirical model is used to model the decrease in the elastic modulus. The strength is modeled to decrease based on an increase in the cross-sectional area occupied by the porosity. The precipitate is assumed to contribute to the mechanical properties of bone due to friction generated by the poisson’s contraction of the organic as it carries axial loads. The resulting stressstrain curve predicted by the model resembles the stress-strain curves obtained in the experiments.