Nano-particles in the range of a few tens of nano-meters that agglomerated into larger clusterswere observed for both Bio-cal-A and Bio-cal-H (Figure 4a,b). After the calcination of these powders, larger crystals or grains with the sizes of a few hundred nano-meters were formed (Figure 4c,d) as a result of crystal growth at an elevated temperature. The results were in agreement with XRD data that showed significant peak narrowing along with sharp increasing in peak intensity of the calcined bone powders. The crystal sizes of samples with 9-h calcination (not shown in this article) were similar to that of 6-h calcination samples, which were supported by their nearly identical FWHM of direction patterns shown in Figure 3.