This paper presents a study of the effect of heterogeneous/homogeneous nucleation and microgravity on the structural synergy between Ca minerals and substrates. The structure of human bone is determined to a large extent by the turnover of the bone, which includes nucleation of biominerals adjacent to collagen molecules. Heterogeneous-like nucleation will promote a strong structural correlation between biominerals and substrates. This may lead to a compact bone structure. On the other hand, homogeneous-like nucleation will create a poor correlation between biominerals and substrates. This may lead to a porous bone structure. Microgravity will suppress convection, and consequently promote homogeneous-like nucleation during biomineralization. This could be responsible for the formation of the porous structure of bone in space.