Published online by Cambridge University Press: 21 February 2011
This paper presents a detailed investigation of the hierarchical and structural organization of the collagen-based aggregates in ivory. Ivory from African elephants is selected as the prototype in this study. A sophisticated architecture composed of collagen fibers and hydroxyapatite-like particles is revealed by optical microscopy, scanning electron microscopy and transmission electron microscopy. X-ray diffraction and TEN with selected area diffraction are employed to analyze the structure. Electron spectroscopy for chemical analysis and infrared absorption spectroscopy give information about the composition and chemical environment of the atoms in ivory. It is found that the structure of ivory has a three-level hierarchical organization, which includes both organic and inorganic materials. In the structure the inorganic material exists inside an organic framework, located outside of the collagen fibrils in the extrafibrillar volume. This inorganic structure has a polycrystalline form. Both the chemical compositions and the chemical environment of the atoms in the hydroxyapatite-like particles in ivory are different from those in natural hydroxyapatite.