Amorphous and Crystalline Phases in Biominerals

  • M. G. Taylor
  • K. Simkiss
Conference paper

Abstract

Many discussions of biominerals are concerned with the formation of calcium phosphate phases and their transformations from amorphous phases to a stable crystalline form, such as apatite with various lattice substitutions [1,2,3]. Other biominerals remain amorphous notably biogenic silica [4], some calcium carbonate deposits [5] and inorganic phosphate deposits found in many invertebrates [6]. The intracellular deposits found in the hepatopancreas of the snail Helix aspersa are an example. They are amorphous and have a mineral composition of calcium magnesium pyrophosphate with ca 18% water giving a formula of CaMgP2O7.3H2O. Organic material, 5% w/w is also present [7]. A feature of these granules is their ready accumulation of dopant cations such as Mn, Fe, Co and Zn. The in vivo doped granules always remain amorphous to X-ray and electron diffraction techniques. The local atomic structures around Ca, Mn, Fe, Zn and P [8,9,10,11,12] have been determined by X-ray absorption spectroscopy using the Synchrotron Radiation Source at the SERC Daresbury Laboratory, UK. An open hydrated structure around calcium was deduced from EXAFS (Extended X-ray absorption fine structure) and density measurements [8] and it was proposed that the granules could be modelled by a modified continuous random network with metal ions cross linking the pyrophosphate chains with the water contributing to the interchain structure to allow the percolation and reaction of dopant cations [13].

Keywords

Phosphates Graphics Calcium Magnesium Aluminium 
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Copyright information

© Springer-Verlag Tokyo 1991

Authors and Affiliations

  • M. G. Taylor
    • 1
  • K. Simkiss
    • 1
  1. 1.School of Animal and Microbial Sciences, AMS BuildingUniversity of ReadingReadingEngland

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