Bone is a matrix of organic matter supported on a mineral scaffold. Bone mineral (biological apatite) contains an abundance of calcium, as we all know, but is mostly phosphate by weight. Phosphate is an anion formed from one phosphorus atom bound to four oxygen atoms – the oxygens try to keep as far away from each other as possible, and give phosphate a tetrahedral arrangement. Although the oxygens are tethered to the central phosphorus atom, they are free to move, and move they do. Oxygen dance moves are well choreographed and can be prompted under the right conditions. For example, all of the oxygens can stretch away from the phosphorus at the same time (ν1), or they can all bend in the same direction (ν2), or two can stretch while the other two contract (ν3), or two can bend one way while they other two bend the opposite way (ν4). Each of these dance moves is called a vibrational mode, and may be induced when phosphate is irradiated with a laser. Over the next few posts I will explore how these vibrational modes report important information about the preservation of fossils.
Smith, E. and Dent, G. 2005. Modern Raman Spectroscopy, a practical approach. John Wiley and Sons (Chichester). Find it on Google Books