Using light to describe the ancient world

Vibrational modes (dance moves) of phosphate.

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.

Recommended reading

Smith, E. and Dent, G. 2005. Modern Raman Spectroscopy, a practical approach. John Wiley and Sons (Chichester). Find it on Google Books


Comments on: "Spectroscopy of fossil bone Part 1: Phosphate" (3)

  1. […] absorbed by your sample, where specific wavelengths are absorbed by specific vibrational modes (see #Spectroscopy of fossil bone Part 1). In other words, a near infrared spectrum gives you the molecular components in your sample: […]

  2. eric larson said:


    Cool site! I was wondering if you have a specific reference for the phosphate vibration modes?


    • Hi Eric, thanks for your interest – I use two references for the phosphate vibration modes:
      1. Kravitz, L.C., Kingsley, J.D., and Elkin, E.L. 1968. Raman and Infrared Studies of Coupled PO4−3 Vibrations. Journal of Chemical Physics 49:4600-4610 (doi: 10.1063/1.1669918)
      2. de Aza, P.N., Santos, C., Pazo, A., de Aza, S., Cuscó, R. and L. Artús. 1997. Vibrational Properties of Calcium Phosphate Compounds. 1. Raman Spectrum of β-Tricalcium Phosphate. Chemistry of Materials 9: 912–915
      (doi: 10.1021/cm960425d)

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