Structure, morphology, composition and organization of biogenic minerals in limpet teeth

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Abstract
The structure, morphology, composition, and organization of inorganic solids in the radula teeth of the limpet Patella vulgata have been studied by electron microscopy, electron diffraction, and e.d.X.a. of fractured, acid-treated, and sectioned tissue. Minerals first appear in the tooth base and comprise: amorphous and poorly crystalline granular, particulate, and sheet-like phases of variable composition (Fe, Si, P, Ca); irregular laths of crystalline goethite; and single crystals of prismatic goethite. The presence of localized Si and P may inhibit goethite crystallization in many regions of the tooth base. Mineralization of the tooth cusp begins with goethite impregnation of the posterior region. Crystals are deposited in the form of thin fibrous strands (15-20 nm width) with the [001] crystallographic axis initially parallel to the posterior tooth wall. Mineralization proceeds by an increase in the number and thickness of the crystals within the posterior region. In contrast, the anterior zone is only partly impregnated with crystals aligned parallel to the long axis of the cusp. The mature crystals are well ordered, acicular in morphology but with extensive growth distortions, and organized along regularly interspaced (30-50 nm) electron-dense filaments within the cusp. Removal of iron reveals the presence of silica-impregnated fibres, folded sheets, and tubular structures (often 30-60 nm in diameter) within essentially intact teeth. We propose that goethite crystallization and organization is regulated, in part, by spatial constraints established by an ordered filamentous organic matrix and that silica impregnates the matrix components at a later stage in mineralization thus maintaining the structural integrity of the organic tissue.