TRACE ELEMENTS IN RECENT AND FOSSIL BONE APATITE

Abstract

The biomineral component of bones and teeth is synthesized within the body, under direct physiological control, and therefore the chemistry of bone (including the trace element chemistry) reflects aspects of the animal’s biology, particularly the trace metal load, but also the state of metabolism of specific trace metals. Bone mineral is relatively reactive due principally to its small crystal size, and consequently bone is unstable once removed from the body. Bone undergoes a complex set of diagenetic processes post mortem, which generally lead to dissolution, however bones and teeth are relatively common components in (post-Ordovician) rocks. The trace element content of bone is susceptible to alteration immediately upon exposure, and while these changes reduce the usefulness of ancient bone as a monitor of the physiology or diet of ancient animals the trace element composition of ancient bone can yield useful paleoenvironmental information. This chapter is concerned principally with archaeological and geological applications of trace element chemistry of bone, rather than physiological or medical implications. The inorganic (mineral) component of bone is carbonated calcium phosphate (Ca10(CO3,PO4)6(OH)2), similar to the mineral dahllite. The calcium phosphates form the vast majority of all vertebrate hard tissues (Young and Brown 1982), and exhibit a very wide range of physical and chemical properties. Stoichiometric hydroxyapatite is not known biologically, and is only produced artificially or geologically at high temperature and pressure. The mineralogy of bone, dentine, and enamel is reviewed in Elliott (this volume). Kohn and Cerling (this volume) highlight the fact that apatite crystal size and shape varies between bone and enamel, and point out that variations in crystal size are in part responsible for the greater diagenetic susceptibility of bone compared to enamel. Bone crystallites are essentially plate-shaped, with average dimensions of 350–400 A × …