Revisiting the inorganic component of bone: beyond the accepted concept of "mineral".

Bone is widely believed to be constructed of apatite with a composition close to that of hydroxyapatite. The mineral of bone is a made up of polycrystalline 5 nm-thick plates of a monoclinic crystal with a composition like that of apatite but differing from that mineral in most significant respects. Although it is a well-defined crystalline species with diagnostic shape, size, composition range and symmetry, it is not a new mineral because it is not known to grow in any known geological environment. It appears to be a different crystalline phase from apatite.