Any improvement in our knowledge of the mineral structures formed by living organisms contributes to a more accurate analysis of their fossil remains. Such a simple remark is important, because selection of the methods used for assessing the preservation of any fossil, as well as interpretation of numerical values resulting from measurements carried out on fossil material, depends heavily on concepts regarding its original state and mode of growth. In corals, for instance, the amount of confidence in the reliability of isotopic or chemical measurements has long been based on a simple X-ray diffraction diagram, owing to postulation of a purely mineral composition of these “physiochemically” crystallized materials.
As defined by Berner (1980) the term “diagenesis,” as applied to any sedimentary object, refers to “the sum total of processes that produce changes – mineralogical, chemical and physical – from the time of deposition.” Such an extensive definition (see also Bates and Jackson 1980) obviously includes fossilization, the term we use when sedimentary processes are modifying materials that have been formed by living organisms. From this standpoint, the methods by which the three major biomineralization mechanisms control the deposition of their mineralized structures allow us to assume that diagenesis of the resulting materials will follow very different and specific pathways. A major difference from chemically precipitated crystals is that biominerals exhibit very distinct structural parameters at the micrometer and submicrometer scales, even if the chemical compositions of their mineral parts do not greatly differ from purely chemical equivalents.