0000000000301151
AUTHOR
Emil Zolotoyabko
Differences between Bond Lengths in Biogenic and Geological Calcite
8 pages; International audience; We used high-resolution neutron powder diffraction to accurately measure the atomic positions and bond lengths in biogenic and geological calcite. A special procedure for data analysis was developed in order to take into account the considerable amounts of magnesium present in all the investigated samples. As a result, in biogenic calcite we found some atomic bonds to have significantly different lengths as compared to those in geological calcite, after the contribution of magnesium is accounted for. The maximum effect (elongation up to 0.7%) was found for the C−O bonds. We also analyzed changes in frequencies and spectral widths of normal vibrations of carb…
Anisotropic lattice distortions in biogenic calcite induced by intra-crystalline organic molecules.
9 pages; International audience; We have performed precise structural measurements on five different calcitic seashells by high-resolution X-ray powder diffraction on a synchrotron beam line and by laboratory single crystal X-ray diffraction. The unit cell parameters a and c of biogenic calcite were found to be systematically larger than those measured in the non-biogenic calcite. The maximum lattice distortion (about 2.10(-3)) was detected along the c-axis. Under heat treatment above 200 degrees C, a pronounced lattice relaxation was observed, which allowed us to conclude that anisotropic lattice swelling in biogenic calcite is induced by organic macromolecules incorporated within the sing…
A hydrated crystalline calcium carbonate phase: Calcium carbonate hemihydrate.
Hydrous CaCO 3 gets a new structure Calcium carbonate (CaCO 3 ) forms important minerals on Earth and is a model system for understanding crystal nucleation. Three different structures of CaCO 3 are known, along with two structures that are hydrated. Zou et al. found a third hydrated CaCO 3 structure formed from amorphous CaCO 3 in the presence of magnesium ions. The discovery illustrates the importance of amorphous precursors for producing new materials. Science , this issue p. 396
Protein-induced, previously unidentified twin form of calcite.
Using single-crystal x-ray diffraction, we found a formerly unknown twin form in calcite crystals grown from solution to which a mollusc shell-derived 17-kDa protein, Caspartin, was added. This intracrystalline protein was extracted from the calcitic prisms of the Pinna nobilis shells. The observed twin form is characterized by the twinning plane of the (108)-type, which is in addition to the known four twin laws of calcite identified during 150 years of investigations. The established twin forms in calcite have twinning planes of the (001)-, (012)-, (104)-, and (018)-types. Our discovery provides additional evidence on the crucial role of biological macromolecules in biomineralization.