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Nucleation and growth of calcite on native versus pyrolyzed oyster shell folia
Sikes, C.S.; Wheeler, A.P.; Wierzbcki, A.; Mount, A.S.; Dillaman, R.M. (2000). Nucleation and growth of calcite on native versus pyrolyzed oyster shell folia. Biol. Bull. 198: 50-66
In: Biological Bulletin. Marine Biological Laboratory: Lancaster, Pa. etc.. ISSN 0006-3185, more
Peer reviewed article  

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Keyword
    Marine

Authors  Top 
  • Sikes, C.S.
  • Wheeler, A.P.
  • Wierzbcki, A.
  • Mount, A.S.
  • Dillaman, R.M.

Abstract
    The thin sheets of calcite, termed folia, that make up much of the shell of an oyster are covered by a layer of discrete globules that has been proposed to consist of agglomerations of protein and mineral. Foliar fragments, treated at 475°C for 36 h to remove organic matter, were imaged by atomic force microscopy (AFM) as crystals grew on the foliar surfaces in artificial seawater at calcite super-saturations up to 52-fold. Crystals were also viewed later by scanning electron microscopy. After pyrolysis, the foliar globules persisted only as fragile remnants that were quickly washed away during AFM imaging, revealing an underlying morphology on the foliar laths of a tightly packed continuum of nanometer-scale protrusions. At inter-mediate supersaturations, crystal formation was seen immediately almost everywhere on these surfaces, each crystal having the same distinctive shape and orientation, even at the outset with crystals as small as a few nanometers. In contrast, nucleation did not occur readily on non-pyrolyzed foliar surfaces, and the crystals that did grow, although slowly at intermediate supersaturations, had irregular shapes. Possible crystallographic features of foliar laths are considered on the basis of the morphology of ectopic crystals and the atomic patterns of various surfaces. A model for foliar lath formation is presented that includes cycles of pulsed secretion of shell protein, removal of the protein from the mineralizing solution upon binding to mineral, and mineral growth at relatively high supersaturation over a time frame of about 1 h for each turn of the cycle.

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