On the mineral components and the remnants of organic structures in shells of fossil molluscs

Abstract

SUMMARY In studies with the electron microscope on the structure of the remnants of the organic components in fossil shells, the nature of the alterations undergone by the mineral constituants associated with these remains in the shell architecture has been determined by X-ray powder diffraction analysis. The present note reports the results collected in 240 powder samples from the shells of 180 species of Paleozoic, Mesozoic and Cenozoic molluscs, mostly Cephalopods and Pelecypods. In this material, 73 species have been so far investigated with the electron microscope concerning the content in organic remains of their shells. Except in a few cases, fragments of reticulated sheets of nacreous conchiolin with the texture of their pattern variously altered were consistently observed in the specimens. These fragments were detected, not only in shells in which the original aragonite had been preserved, but also in samples in which it had been recrystallized into calcite or replaced by other minerals. Some alterations in the nacreous reticulated sheets of conchiolin are described and illustrated in one Nautiloid, two Ammonites and nine Pelecypods, including Trigoniidae and Inoceramus.