AbstractsEarth & Environmental Science

Bone is composed mainly of mineral and collagen. The mineral, bioapatite, is a form of carbonated hydroxylapatite, which makes up over 50 wt.% of bone. Mineralogical features of bioapatite, e.g., chemistry, mechanical properties, degree of crystallinity, and morphology, thereby absorb mineralogists' interest. However, normal bone contains much collagen, which is interlaced with mineral crystallites at the nanometer and micrometer scale, making the study of bioapatite very difficult. In addition, removal of the collagen by chemicals usually changes some chemical and physical features of bone mineral. Hypermineralized bone with extremely high mineral contents (>80 wt.%) fortunately allows the application of many analytical techniques to investigate the mineralogy of bioapatite with very little interference from collagen. Therefore, such hypermineralized bones appear to be the ideal materials in which to study bioapatite in bone. In the present study, a rostrum bone from a Mesoplodon densirostris whale (~96 wt.% mineral) and bullae (ear bones) from Tursiops truncates dolphins (~85 wt.%) are analyzed by several techniques, e.g., Raman spectroscopy, electron microprobe, and scanning electron microscopy, to investigate the mineralogy, to compare hypermineralized bone to enamel, and to distinguish age-related changes of the bioapatite in bone. Firstly, it is necessary to confirm that these hypermineralized materials are true bone, rather than hypermineralized enamel or other dense bio-tissues. The Raman spectra of the rostrum and bullae show similar peak occurrence as in other normal bones, except for the low intensity of peaks for organics. Raman spectra also confirm that the mineral in the rostrum and bulla is carbonated hydroxylapatite, just as in other normal bones. A set of bone features, e.g., collagen fibrils, lacunae, osteons, vascular holes, and blood vessels, are identified in the rostrum. The dolphin's bulla has long been recognized as true bone because it is actually the ear bone. However, these two types of hypermineralized bone show distinct processes of mineralization. The high density of the bulla results from complete filling of the inter-trabecular spaces with hypermineralized tissue, whereas the rostrum undergoes hypermineralization during extensive remodeling and development of secondary osteons. Secondly, the hypermineralized rostrum, as a bone exemplar, was used to investigate the chemistry of bioapatite. Relatively few chemical analyses of major and minor elements of bone mineral have been reported. The existing analyses are usually based on ashed bone and therefore do not exclude effects from the abundant collagen. Electron microprobe analyses of the rostrum's bioapatite show an average carbonate content of ~8 wt% and an average Ca/P atomic ratio of 1.7. Electron microprobe and Raman analyses show a homogenous distribution of the mineral content, except around a few vascular holes and vessels. Hydroxyl depletion in the bioapatite is coupled with carbonate substitution and Ca can be substituted by Na…