We report the first simultaneous quantification of Young’s modulus in the separate material phases of bone: collagen and carbonated hydroxyapatite. High-energy X-ray scattering and in situ loading revealed macroscopic, mineral, and collagen Young’s moduli (90% confidence limit) for a canine fibula equaled 24.7(0.2) GPa, 38.2(0.5) GPa {for 00.4 and 43.6(1.4) GPa for 22.2}, and 18(1.2) GPa, respectively. The mineral contained compressive residual stresses on the order of −60 to −80 MPa before loading and had a stress enhancement (ratio of internal to applied stress) between 2.0 and 2.3. The diffraction peak width increased with increasing applied stress, mainly along the bone’s longitudinal direction, and peak widths returned to pre-deformation values when load was removed. In a second fibula section from the same animal, the mineral’s internal stress changed from −50 MPa (22.2 reflection) to −75 MPa (00.4) just after removal from formalin to −10 MPa after eight hours immersion in phosphate-buffered saline; the corresponding change in collagen D-spacing Δ D/ D equaled 4.2 × 10 −3.