The nanoindentation technique was used to characterize the indentation modulus of intramuscular herring bone (Clupea harengus) along its length, from early to fully mineralized regions. Both the indentation modulus and modulus anisotropy ratio, indentation modulus longitudinally/indentation modulus transversely, increased nonmonotonically with mineralization, from 1.1 in the early stages of mineralization to 2.1 in the fully mineralized region. The indentation modulus in the fully mineralized region decreased from 19.9+/-2.0 GPa in the longitudinal direction to 11.4+/-1.5 GPa in the transverse directions. In the earliest stages of mineralization, the indentation modulus was 3.8+/-0.7 GPa in the longitudinal direction and 3.5+/-0.3 GPa in the transverse direction. High-intensity synchrotron x rays were used to examine two parameters of crystal texture, the coherence length and the angular spread. Low angular spread was seen along the c axis of bone crystallite. However, the large angular spread observed along the (300) plane indicated an imperfection of crystallite periodicity in the direction perpendicular to the longitudinal axis in the bone. The relatively high coherence length was related to the low angular spread. In general, the indentation modulus increased with increasing crystallite size, but the indentation modulus decreased with increasing crystallite size along the (300) plane.